I have been "piloting" a 64 bit vista machine and the issues have been
extreme. As you know, many companies are slow to support a vista version or
even not planning on doing it at all, there are even more such issues with
64bit vista. Vista64 fails to support many file "infrequently used" file
types. FOr example, MICROSOFT live meeting wont work on 64bit Vista because
uploading resources to the live meeting server requires conversion to a
special file extension that vista64 does not support. Live meeting support
has stated that they have no intention of attempting to correct this issue on
their current release of the software. One of the major shipping companies'
packaging softwares wont run on 64bit. Real player software didnt work on 64
bit as of 2 months ago but that may be corrected now. The point is that while
converting to vista means some compatibility issues, converting to 64bit
makes it 10 times worse. I like the way vista works, and to be honest, the
32 bit system I use seems to run just as well as the 64bit at long as you
have a gig or more of ram.
Personally, unless you really need the 64bit processing for something
specific, you wont see any major difference in performance and just a lot
more conflicts.
But if you want to go 64, you will need to do a clean install since you cant
upgrade from 32 bit to 64. Depending on your licence that could require
buying a new copy of the software.
