For retronauts who wants a modern OS on decidedly sub-modern CPUs but don't want to go the Linux route, Windows 7 is looking to be a juicy plum. It seems to be excellent at scaling... far better than Vista was.
That makes sense, of course: when Vista was being developed, no one at Microsoft had even thought that a big part of the future of computing might not be in beefier hardware, but cheaper and lower-power architecture like the Atom. But that rationalization doesn't change anything: Vista honks choad on anything below a gig of RAM and a couple of gigahertz.
Not so Windows 7. They've made some great optimizations to the point that it can run on a 600MHz A100 processor via the Amtek U560 UMPC. I really need to give loading the Windows 7 beta on a netbook a try.