My desktop is an eMachines, slow, basic, simple, but enough for what I do. It runs XP Home. If I want to upgrade this system to 7, I can either spend $200 for a retail version or $109 for an OEM, and buy a new hard drive to install it. That ties it to the motherboard. I don't want to do that. So I think this will become the kid's computer and I'll build something new and put 7 on that. AM3 board, DDR3 memory, ability to Crossfire, something nice and new and future-proofed as best I can.
My wife's computer OTOH is a beast. Core i7-920, overclocked to 3.5, a HD4870 video card, 6GB of memory, and it runs the 7 Ultimate RC. We're spending the $319 to put a full retail version on it in February, because the RC expires in March. It's been worth it. Everything about 7, she loves it. And she hated Vista. So it's very good for her and eventually when I have a decent machine, it'll be good for me.
I hope SP1 comes out before then. In fact I WILL wait until a service pack is released before I build a computer to use 7.