Another udate from me:
Well, today after installing Liquorix 2.6.34 kernel for Debian and visiting launchpad.net with Chrome and Firefox I completely got rid of any slowness. Liquorix
kernel is known for its performance optimization and is based on zen
It is definately not an NVIDIA issue.
debian i686 squeeze/sid
P.S. Something is really wrong with the i/o scheduler in the recent linux kernels. I noticed some time ago, especially when copying a large file (=> 1 gigabyte) and trying to do something simultaneously with the system... There is a regression somewhere. People advise to use BFQ scheduler (Liquorix and zen have it already patched and compiled into the kernel). By default there is no BFQ in the vanilla kernel. You need to patch it or use one of these (zen or liquorix).