I beat you all!
Just for the fun of it (please, don't flame me) :
I'm still using system 7.1 on my 10 years old machine, with 32 MB of RAM and a 500 MB HD, 68040 processor. I'm using many apps, like Photoshop (I don't remember which version). Many well selected extensions. And guess what ? It rocks ! This machine is robust, fast, efficient, very stable and never crash (well, almost).
Ok, I can't play games, or even go on the internet. But for all my serious job...