well from what i gathered from the manga about her, she isnt in the least annoying... however myself being a guy, its pretty hard for me to find a girl that actually irritates me. but i see other guys in anime/manga that i immediatly have a problem with, even if theres girls saying they hot n stuff lol.
I don't think she's annoying.. I mean she's not led on very much about anyone liking anybody except when she liked Kaname.
I wish Yuki's character could be a little bit more like.. any other girl's in a way, though. Her character is kind of... empty, and hard to relate to.
Other than that, I have no problem with her. and it's not like she's completely weak, she's brave most of the time it just that someone comes to save her before she does anything sometimes..