I would use my AmigaOne most of the time, but unfortunately it's just not possible to do a lot of the things I wanna do, and a 2.7GHz Core2Duo with 4GB Ram and XP is what I use for my "main computer". I try not to use it whenever I can, but for general web browsing it's less stressful, and things like Photoshop, colour calibration for the display, scanner and printer, a decent office suite and being able to use my printer properly are all things I couldn't do without. I also try to use Linux whenever I can, and while it does as well as, Windows at some tasks, they more often than not require more effort to get there.
