In terms of 4.5, I'm all over it. I did manage to find a computer to install it on and I'm impressed already. Plus there's some exciting developments hidden away in there that I won't be able to get to grips with until I have it on my main frame (highlights in Richard's post here—e.g. geometry shell). But I won't be upgrading until Reality is ready—and maybe Gen X (but I think I can live without that for a while).