In the Entertainment Weekly Popwatch blog:
Why "The Ex List" was doomed. The comments suggest that the show failed for reasons from the annoying lead to the bad time slot. That last suggestion was close, but I know the real reason.
It's not just the time slot, it's THAT time slot. It's cursed. The Friday 9-10 p.m. Eastern time slot on CBS is the Defense Against the Dark Arts professor of television. In the past few years it's been through at least five shows: Moonlight, Robbery Homicide Division, Close to Home, The Ex List, and that Price is Right big prize game, though I'm not sure that was meant to be anything long-term. For CBS, it's not Friday night all around, it's just that time slot. The shows on either side of it, Ghost Whisperer and Numb3rs, are fairly successful, all things considered. Given the success of those two shows (Numb3rs was a midseason replacement that's now in its fifth year), I can only conclude that if you're on a show in CBS's 9-10 p.m. Friday time slot, you'd better be polishing your resume. See, even
Wikipedia agrees with me! Sort of.
(Seriously, I'm joking about the time slot being hexed, but I don't have a better explanation.)