Windows XP Professional x64 went RTM (i.e. went gold, in Microsoft jargon) on April 25th 2005. For those with Windows XP Professional and a 64-bit capable system, you can order your x64 "upgrade" online. The reason for the quotes is because you must do a fresh install (it's evident if you think about it: 32 -> 64) rather than just upgrade on top of your existing install. Personally, I do fresh installs even when the option of upgrading is available.
I installed x64 yesterday. From installation to use, it feels identical to the regular 32-bit edition save the name. One might think this is fairly obvious, as the user interfaces and everything else should remain identical since it's still Windows XP, just that it's 64-bit. This is not true however; the x64 is built upon Windows Server 2003 code, not Windows XP.
Installation was fairly painless, but x64 did not install my graphics card (GeForce 440 Go) and audio chip (ADI 1981B). After searching around the 'net and settling for some beta release drivers, I finally got both these essential system to work. My laptop's fan seems to be going off a lot more frequently and some of the indicator lights act strangely. At least the video and audio drivers are stable..
Now, on a positive note, the performance thus far has been amazing. I used to run Guild Wars (GW) in 1280x800 on the lowest settings, and even then the framerate was less than adequate. However, now I run GW in 1280x800 on the highest settings and it's liquid smooth!
I was quite shocked: I expected a decrease in performance since GW does not support 64-bit goodness and instead is a native 32-bit application - meaning it has to be emulated. x64's emulator is named WoW64 no less =P. So far all my 32-bit applications have been running better than before, so this the first emulator I've seen that is more efficient at running applications than their native environment :) Keep in mind that I'm keeping the hardware capabilities constant.
Anti-virus software was a tad difficult to find for the x64 platform, but I eventually found one that had this funny registration message:
IMPORTANT NOTICE: The free registration of avast! 4 Home Edition is performed by a robot which sends the message containing the license key to the email address you entered in the registration form.
Awesome, go robots! :P
Also, as I was looking for a new place to find torrents after the demise of suprnova.org, I came upon this site called "The Pirate Bay". The best part I've found about this site is their "Legal" section =P. Take a look when the mood is light.