Well, no system is completely safe or perfect. However, I feel that Mac OS X in particular comes very close to my personal understanding of perfect. That is one reason why I switched to Macs. Also because everything just works for me, I have never seen a Mac crash with the things I do, while on Windows it crashed a lot. Yeah I know what they say, it always depends on the user and how he's doing things. But in my case, I do the same and now more demanding stuff, and so far, none of my Macs has crashed. So for me: I stick with Apple.
Besides that, iPhoto is doing fine for me in both machines with 1 Gig RAM each. But I also have to add to that that I don't have more than 900 pictures I think. And iPhoto did not crash on me so far.