Well, I’ve spent a few months running 64bit slackware and WinXP 64, and I have to say that neither OS is production ready. The basic functions of each OS work, mostly, but backward compatibility and third party software support are both less than stellar.

Windows

• Services for Unix (SFU) has not been, and will not be, ported to XP64.
• x86-64 programs are put in C:\Program Files, and 32bit programs are put in C:\Program Files (x86). Many old windows programs (including the steam installer) can’t handle parenthesis in a path.
• NVidia’s windows x86-64 driver installer doesn’t support my gf4 ti4600, although modifying the .inf file allows it to install and run fine.
• Useful things like Daemon Tools don’t work because of driver format changes.
• A bunch of little things I don’t remember right now

Linux

• /usr/lib and /usr/lib64 confuse some programs<
• Some poorly written software (like mplayer) assume 32bit pointers
• Shell script game installers blow up very, very badly. So badly, in fact, that I’ve been unable to run any of my native games (Q3, UT, UT2k3, etc)

Since all the things I really care to use Spaceheater for don’t work or work poorly, I think I’m going to go back to real Slackware, and 32bit Win2k or XP. Thankfully AMD did a great job with their x86-64 design and implementation, so I shouldn’t notice any type of a performance hit, and I don’t have 4GB of memory to worry about using anyway.

Unless you’ve got a need for 4GB+ of RAM and can’t use a better architecture, then stick to 32bit OSes and give the 64bit stuff a few more years to gel. That recommendation doesn’t apply to hardware of course. AMD’s 90nm Venice core can run in 32bit mode just fine, has SSE3 support, and runs at room temp with a slow, quiet fan. Plus you’ll be ready for when the software finally IS ready to run in 64bit mode.