Nope - if I hear that the ending was awful, I won't pick up the series. If the finale is suckish, then it usually ruins the entire thing for me.
It's kind of annoying, because I know there are some good manga/anime out there that I won't touch because I know the ending stinks...
Spoiler (highlight to view)
Slam Dunk, Ichigo 100%...I know there's more, but the names escape me at the moment
On the other hand...if I'm already a good way into the series when I find out about the bad ending, I'll finish it. I'll never re-read it, but I'll finish it. But I've never yet found a manga that was so fantastic that even an awful ending couldn't ruin it.