Look for drivers for your hardware to see if everything is 64 compatible. For apps, many apps run with no issues, many do not - like stated above, depends on the app. From the different Vista forums, the vast majority of people have issues with apps not being 64 bit compatible and for that reason alone they are sticking with 32 bit (especially for gaming) until 64 matures. However, a very small but growing segment of people are running 64 bit and finding alternatives or stopped using non-compatible apps.