The characters for Kirisame literally mean "drizzle" or "misty rain". Marisa doesn't make much sense though... the first character means "magic", the second "logic" or "reason", and the third "sand". There is large amount of speculation on the extremely controversial theory that "Marisa" is, in fact a given name with possible origins in the romantic language family (see http://en.wiktionary.org/wiki/Marisa). However, the Western name theory does have a lot of logical backing, as Marisa is a mix of Eastern and Western culture, plus Western names aren't unheard of in Japan.
Moreover, "Witch of Love Potion", originally the stage theme from the obscure game Torte le Magic of which ZUN composed the three-tracks-long soundtrack, but arranged in Dolls in Pseudo Paradise, albeit having no initial relation to Marisa at all, may go in the favor of that image ; not to mention the ambiguous backstory of this song talking about an unnamed person secretly buying a love potion.
As Reimu is often referred to as red-white or "the red-white", fans frequently call Marisa black-white or white-black in parallel.
Marisa is one of the most frequent characters to appear in the Touhou series, tied with Reimu after the release of Fairy Wars.
Marisa has 6 theme songs (excluding remixes), more than any other character in the series.
Despite her self-indulgent personality and lack of concern for others (or more likely because of these things), Marisa happens to be one of the most popular characters with fans, winning a 2005 Touhou popularity contest.
In the game Shuusou Gyoku of the Seihou series, Marisa shows up as the first boss of the Extra Stage. However, she is sporting wings akin to Flandre Scarlet as well as a technique that allows her to duplicate herself. Shuusou Gyoku also predates Embodiment of Scarlet Devil by two years.
She is known for "copying" attacks from enemies she has fought, namely Non-Directional Laser from Patchouli and Master Spark from Yuuka Kazami. Additionally, the green projectiles that she fires as a playable character seem to have been lifted from Reimu (see SoEW) and the overall astronomy theme to her magic seems to have been learned from Mima (see SoEW when Marisa served Mima - Mima used Orreries Sun during the last boss fight). Moreover, she used Alice's Artful Sacrifice as reference for her Shoot the Moon spellcard.
Marisa has a hobby of collecting things, whether they already belong to someone or not. It is stated that she never throws away anything she collects, which results in her house being the messiest in Gensokyo. However, she seems to collect items without knowing their true value; Rinnosuke once finds an ancient sword, namely the famous Kusanagi-no-Tsurugi in a pile of scrap metal she owns.
Marisa is always depicted in her game sprites as riding on her broom when she flies (typical witch behavior). Whether she actually needs her broom to fly or if it's just for show is unconfirmed.
However, in Fairy Wars, her broom is nowhere in sight. This hints to us that she may be able to fly without it. (Or the artist merely couldn't put it into the sprite)
The fuel for most of her magic are phantasmal mushrooms, and the fan-made game Super Marisa Land features many, many Super Mario styled mushrooms.
Despite being a western style magician and fitting the classic image of a witch, Marisa's most precious item is an eastern style Hakkero: a mini furnace in the shape of an octagonal block with the eight trigrams printed in a circle on its front. Despite its small size (it fits easily in the hand), it is a potent source of magical energy and has the firepower to burn down a mountain. Marisa usually uses it like a normal furnace and treats it with good care. It is the only treasure Marisa collected that is used and taken care of on a regular basis. Marisa is frequently depicted using the Hakkero to power her Master Spark. The original Hakkero was an item in the Chinese classic "Journey to the West", where it was used by gods to create spiritual medicine.
Marisa may be somewhat of a math genius; in Mountain of Faith she utters the line "I could recite all the digits in pi before I got there." However, considering that pi has a literally infinite number of digits which never end or repeat in any pattern (really, it's endless), it's likely just an expression to say "at this rate I'll never get there." She also knew the number of times she had eaten bread off the top of her head when she originally confronted Remilia in Embodiment of Scarlet Devil.
Marisa holds the distinction of being one of the very few characters in any Touhou game who is known to have a living family. They've never been mentioned by name, or even within any of the game dialogues, but it is implied in Perfect Memento she is the only daughter. Also according to 19th chapter of Curiosities of Lotus Asia her father, at least, is alive and is living at the Human Village.
In Imperishable Night Marisa survives looking at the full moon, which should drive normal humans insane. When Alice asks if she is all right, she says that it's all right since she is insane to begin with. She might well be joking, since Reimu and Sakuya maintain their sanity looking at the full moon too. It could be that humans who are strong-willed enough can overcome that influence, or something along those lines. Other fan theories suggest that Sakuya may be Lunarian, Reimu's natural magical aptitude may shield her, and that perhaps Marisa should be taken true to her word.
Marisa often refers to herself as "just an ordinary witch". This is often her character title in the games (i.e. Imperishable Night). Deneb the witch of the Ogre Battle games refers to herself in a similar, yet opposite manner: "I am a witch, but not just an ordinary witch!" She appears to make a reference to this in Perfect Cherry Blossom's third stage, when questioning whether or not Alice is an ordinary human.
In Touhou Hisoutensoku one of her alternative color palettes gives Marisa a blue attire and red hair similar to the purple attire she wore in the PC-98 era (the colors match specifically to her attire color and hair color in Story of Eastern Wonderland). Another alternate color resembles Ellen from Phantasmagoria of Dim.Dream. There is also another palette that gives her a purple attire and purple hair, somewhat resembling Patchouli. And, yet another dresses her in green with blue hair, so she resembles Nitori.
Excluding the fighting spin-offs, Double Spoiler, and Fairy Wars, Marisa's face has appeared on all of the Windows game icons so far. This includes Shoot the Bullet, in which she doesn't actually appear.
There have been several hints that Marisa might become a youkai magician in the future; Akyu comments on the possibility in her Perfect Memento article, and in Undefined Fantastic Object, she becomes evasive when Minamitsu Murasa points out that she's human after Marisa expresses interest going to Makai "as a magician" (though this could be explained by Marisa having tried to claim she was already a youkai).
In Mountain of Faith, when you use Marisa B (Piercing Type), if your power level is 3.00 - 3.95, when you attack a midboss or boss unfocused, their health bar rapidly drops down. Because of this, the opponent is usually defeated before a single bullet even reaches Marisa. Some fans consider this cheating.
Marisa has recently made a "cameo" in Ougon Musou Kyoku, a spinoff of the Umineko series. Jessica added as a recent patch to the game transforms into Marisa's outfit and fires an upward laser that highly resembles her Master Spark for her Meta-Super.
In Scarlet Weather Rhapsody, Marisa's Forward+C attack resembles Goku's Kamehameha from Dragon Ball. Her Skill Card "Narrow Spark" is a stronger version of this attack.