Actually, Windows 7 is quite stable, as they don't add beta features to the OS, so the os is stable, but not feature complete. It's quite useable too it seem, SS uses a Asus netbook with a 1GHz CPU and 1GB RAM, and runs windows 7 on it, and he uses that as his main laptop.
Actually, I've personally used both M1 and M3, and they both run very nicely. Better than Vista, actually.
And as for time-bomb, the smallest time bomb I've ever seen was 90 days, and that's plenty of time to test between leaks.