The nice thing, and this is why I mainly keep these machines around, is that I have a little network going on. I don't do a lot of stuff that requires Adobe's CS6 features exclusively, and I have every different version of CS running on my machines (passed down to me when they threw out the machines, CS6 is my first official purchase/subscription). So my MacBook Pro acts like the host (I only use it when I'm on my bed - I'm lazy, I pretty much do 100% of my work under my covers, lol), and then I can pull out my files if I want to work at my desk with my G5, or if I need to sit in the living room for whatever reason, I can do the same on my iMac G4.
Photoshop, Illustrator, Flash (creating it anyway!
), and Dreamweaver are perfectly fine still. You can't use the new versions, but they're pretty much all the same, except minus all the obscure features that most of us here don't use anyway.
A lot of the really cool apps came out during the Leopard era too. You might have to find the specific versions that work, but there is Evernote, CloudApp, Espresso, LittleSnapper, Pixelmator, AudioHijack Pro, Cyberduck, and a few more that I can't remember at the moment. You can also use something like Fluid to make web apps that open like an actual app to take advantage of thing like Pocket, Cloud Reader, iCloud, etc (I actually do this on my MBP).