I'm with Ficbot, I never leave bad feedback. I usually figure, what's the point, I should have been reading a different kind of book. Plenty of people love the books I hate, and vice versa. And I rarely finish books I don't like, so it's not really fair to leave bad comments about them. Maybe the pace picks up around page 147, like it did with Lies of Locke Lamora.
That said, I'll join MoeJoe in meeting Dan Brown in the ring any time, and I'll fight dirty, too!
Re: MoeJoe's comments on writing -- I'm a lot pickier about getting comments on a WIP (that's Work in Progress) than on an already-published book. I don't need random input cluttering up my process.
Stuff that's published, well, I don't actually care what anyone says. It's not like I can do anything to fix them now that they're in print.