I'm a Windows person, and I don't want to switch away from XP. When I recently built a new PC with 4 GB of RAM I had to switch to 64-bit and I had a bit of unpleasant experience with it. Windows XP 64-bit is built upon the codebase of Windows Server 2003 (Vista is Windows Server 2008) and it shows.<p>1. Some hardware may not have drivers for the OS. While on 32-bit system you can connect any device form a decade ago and it will possibly work (with drivers that were also written a decade ago), with 64-bit there's additional possibility of breakage. My printer, HP LaserJet 1015, is manufactured in 2004, but alas, it doesn't have drivers for XP 64-bit. I can get away with installing un-working driver and substituting the driver with LaserJet III's which kinda works. HP's support can recommend nothing better too.<p>2. Same with system software; something might break too, most likely if it is system-related. I have used SwitchIt, a keyboard layout switcher, for a long time. Its last version is from 1996, but it worked fine for me. In 64-bit, it doesn't. (there's a beta version now which kinda works, but what if there wasn't one?)<p>3. Not 64-bit related, but Windows related one. I came to like Hibernate feature in Windows XP, but it stopped working for RAM >= 4GB. It's a known issue: <a href="http://support.microsoft.com/kb/888575" rel="nofollow">http://support.microsoft.com/kb/888575</a> I guess, the person who wrote it left long ago and they can't figure out how to add support for files>4GB, or addressing RAM>4GB at boot time. Seems like other OS folks don't have this problem.