Gene,
I tend to be slow to upgrade, especially in the absence of major improvements. Nonetheless, I went to 6.3.3 and am glad that I did. The major plus is improved speed. The only significant negative was an issue with Adobe Reader 10, which did not occur on machines already using Adobe 9.5 and disappeared on the machines with 10, after rolling back to 9.5.
There has always been so user-to-user variation with upgrade issues, so there is never a guarantee, but I think most will be happy going to 6.3.3.
