Yuuka is thought to be the originator of the spellcard "Master Spark", which Marisa subsequently copied and made famous. Yuuka is also known for the "Dual Spark", two slightly smaller beams fired simultaneously.
Both VIVIT and Youmu have pointed out to Yuuka that her outfit, or Yuuka herself, bears a resemblance to Reimu.
Similar to how Yukari is called "Yukarin," Yuuka is commonly called 「ゆうかりん」 or "Yuukarin". This distinction can be lost in English if her name is spelt as "Yuka" (as in "Yukarin") instead of "Yuuka" (as in "Yuukarin").
Though her exact age is unknown, there are many hints throughout the games and printed works that she's actually an elder youkai who's lived a very long life.
Instead of her distinctive umbrella, she is shown with a baton when she uses a bomb in Mystic Square.
In Mystic Square, Yuuka's player sprite is the only one outlined in blue. In Phantasmagoria of Flower View, she is not. In Yuuka's ending in Mystic Square, she talks about learning magic. This could be that in Mystic Square, she used her power she acquired in her dream world and in Phantasmagoria of Flower View, she used magic plus getting power from the flowers in the flower fields.
Yuuka's known for telling lies most of the time, as canonically shown in her story mode in PoFV.
In the game, Touhou Mother, Yuuka is really relaxed and slow, but a strong fighter.
Yuuka (along with Kaguya and Nue) is one of the few characters that do not wear any type of headgear. However she does wear a nightcap on her head when you first meet her.