I could drum a long list of annoyances if I put my mind to it, but off the top of my head:

-their mobile apps are complete garbage (subtopic in and of itself)
-the input system on the English website (i.e. type "shanghai" too fast and you'll invariably confuse it) drives me nuts

I'll add more as I think of them, and I'll try to balance my rants with positive experiences as well (if I can think of any).

(Btw, I've contemplated starting a ctrip venting thread for some time, but held back out a fear of it being construed as petty.)