NVidia has released a few small bugfix-releases following 177.67, and I gave the 177.70 beta release a try.
Their proprietary driver is especially interesting because it does not depend on EXA (which still has some performance bugs in xorg-server-1.5) and all the memory manager stuff is already in place.
Most Java2Demo tests are accalerated really well now, however the driver seems to struggle with text so nimbus-performance is worse than with the Nouveau driver.
Another weird thing is a software-fallback hit in Java2Demo when using TexturePaint, which I was not able to reproduce with J2DBench at all.
More about it here: http://www.nvnews.net/vbulletin/showthread.php?t=118801
Despite the problems reported NVidia is definitivly doing well.
Hopefully the problems will be fixed in the next few releases, enlarging the types of hardware the XRender pipeline can run on well.