I love them... the herve leger one's are gorgeous.
I think the thing is with body-con dresses, people think because they are tight that they they wont suit you if you're over a size 8. Admittedly, most of the styles of body-con dresses are really flattering to a more 'curvy' figure. But theres still quite a few one's that people up to say a size 14, could get away with. For instance, the black & gold body-con dress that all saints were selling last year, my friend had that in a size 12 and she looked great in it.
Saying that though, there's some horrid styles around... the lycra type one's they've started selling in topshop are awful. But thats probably just me being bitter because Im a size 8, yet I couldnt even get my head through the size 8 of that particular dress!