Well, at this point all I can say for the Nouveau drivers in Fedora 15 is that they are doing an awesome job. I've seen no problem with my everyday use so far. I even got them desktop effects enabled!
I'm glad to see you've got a different card. I guess we can conclude that there at least problems with the 6xxx, 7xxx and GT2xx cards / chips. It would be nice if more people have this problem, then we know at least that it's a serious problem.