As a pro photographer, I use Lightroom and Photoshop CS3 heavily every day on my year-old MacPro, iMacs, and (yes) 4 month old MacMini. I haven't upgraded to PS4 yet, nor have I upgraded to Snow Leopard. PS3 and Leopard are serving me well and I'm not lacking anything... that I know of. Or am I? Is there much compelling reason to bump Photoshop CS3 up to CS4? How about moving up to Snow Leopard as regards compatibility with Photoshop CS3 or CS4? I've been taking a wait & see attitude on these upgrades, and wondering if upgrading either PS or the OS will present any problems which might make me wish I hadn't upgraded. Thanks for the advice.