I have been running xp x64 and love it. I have the same stability as Vista/2003 does (I've run both of those os on my same pc) and I have the driver support of an xp os (wouldn't have even considered x64 in 2005, but in 2007 it is matured to my tastes), and on top of everything, I actually have support for my Audigy, unlike in Vista.
As for sp2 screwing things up, I integrated sp2 into my x64 install with nlite and I've had no problems with x86 browsers not connecting to internet. I also have all the latest hotfixes installed as well. So, Firefox x86, IE x86, and IE x64 all work great, except I have no flash in IE x64, but that is a limitation of Flash.