I don't remember them hooking up on TNG because I'm only on season three, but watching DS9 I would exhale very loudly and roll my eyes every time the "Guest Starring Rosalind Chao" would appear in the credits. Keiko O'Brien is such a god-awful, horrible bitch that has nothing but contempt toward the good Chief O'Brien. Anything he does is met with complete revulsion from her.
I felt really bad for the Chief when Major Kira was carrying Yoshi. You could tell that they had chemistry together, cared for each other, and Chief O'Brien (reluctantly) stayed with Keiko even though he would have been infinitely more happy with Kira.
I also remember the episode where Keiko was possessed by an alien consciousness (I can't remember the name right off), but was thinking even though she was a total bitch, she was still nicer and less sinister than the real Keiko. I was also disappointed when they found a way to bring Keiko back
So, I guess you can say, yep. Keiko O'Brien is a completely unlikable bitch. Hell, I think O'Brien would've been happier hooking up with Kai Winn.