Beta download page. You'll also need a product key which you can get if you have a legit Photoshop CS2 key by going to the Beta Trial page.
Even though I've spent only about 15 minutes with Adobe Photoshop CS3, I already find myself quite impressed. First of all, it's fast. Not only on a Mac Pro, on which it launches nearly instantaneously (as far as Photoshop launches go), but also on a PowerBook G4 on which it opens a lot faster and feels a whole lot snappier than CS2.
The installation process is also a lot more streamlined although this is probably subject to a lot of change before the entire Creative Suite 3 is released. Still, I shall be glad if they keep approximately the same steps because currently it involves very few clicks and it's very easy to get PS CS3 up and running.
One thing I will definitely find useful is a proper uninstallation option in the Setup program (which detects automatically whether the thing is installed on your Mac or not). With suites like Adobe's, which install a bunch of stuff here and there all over your hard drive, a drag-to-trash is very much an incomplete process as far as getting rid of the thing goes. Now that Adobe has added uninstallation as an option, I can forgive them for not using Apple's Installer which currently has no provision for uninstallation (in fact, the only way to uninstall Apple's very own Developer Tools is to manually run a perl script which they provide from the Terminal - most certainly a very inelegant method). Of course, the better way is still to do what Microsoft does with Office which is to design it such that it's contained within its folder in the Applications folder, but I'll take what I get.
What you see above is the default view of Photoshop with an image (one of their samples) open.
And in the picture above, you can see a clever UI feature which allows you to collapse all the palettes when you're not using them. Just look at the screen estate we're saving on a 1024x768 screen like mine! 12" PowerBook and other small screeners will love this (also, if Apple releases the rumoured MacBook Thin in January, perhaps even more people).
Honestly, I'm a shallow person (not to mention lazy) and not even all that involved with Photoshop on a day-to-day basis. The fact that it runs faster on all Macs and natively on Intel Macs is enough to make me use it and that's all I needed from it anyway. If you want actual details about new features in the thing, read Macworld's First Look and Video Preview.