I've not really tried it with any heavy duty apps or processing. I assume they would not be much effected. Its mainly browsing and GUI, OS functionality that's faster. I think more of the OS is multi-threaded than before.
On a slightly separate issue, I've noticed any old single threaded machines people ask me to fix (late P4's Xeons) are almost unusable now, especially on the web. However any dual core machine is still fine. Even with low RAM. I think W8 will breath new life into some of these machines if they are still on XP.