In a cupboard, I've got a G3 233Mhz, 160mb RAM. I really should dust it off. Old OS admittedly, and that spec doesn't sound like much, but it ran like shit off the proverbial - even compared with my newer much 'higher' spec PC stuff. Was always very happy with it, mainly for Cubase, but also Photoshop and other demanding stuff.
I struggle with Macs these days... I think there's a kind of "muscle memory" effect when you get used to an OS. You reach for things, find they aren't there, then get frustrated. I've sat with friends MacBooks and really hated trying to use them. But I'm sure it would only take a few days - Apple's belief in simplicity is still thoroughly alive I expect.