Yesterday I bought the Photoshop 6.0 Upgrade for Macintosh. I was able to use the upgrade because ages ago we bought a flatbed scanner which bundled Photoshop 4.0 for something like an extra $50. The Adobe technical support person I spoke with when confirming that this was a valid upgrade option told me they didn't do such bundles anymore because "it was too good a deal."
This was "too good a deal" as well. If I'd had to pay full price, I wouldn't have bothered. It costs four times as much as the upgrade. But now I've got the modern version installed and fully functional! The layout has changed a lot, and I expect it will take awhile to get up to speed, but I've already discovered a feature which makes this upgrade worth it: constrained cropping. That is, I can tell Photoshop that I want to crop down an image, but that I want the crop to be constrained to say, the dimensions needed for a 4"X6" photograph (for digital printing). It works great, and if I'd had it last weekend it would have saved me an hour when I was creating images to print at the Costco digital imaging kiosk.
I'm gonna try working through the user's guide to find out what features are of interest to me, but I'll probably pick up a book for 'noodling' projects later on. Maybe The Photoshop 6 Wow! Book, or the Adobe Photoshop 6.0 Classroom In A Book.