My Powerbook G4 I use from time to time. Since owning it, I would occasionally wipe it clean, taking it back to OSX 10.2. Increased the RAM to 2GB and it runs well. The only thing that really slow is when I watch 720p videos on youtube. But its slow on my MBP...
No snow leopard but that ok. Tiger is fine. If you think about it, some of the stuff that we use on Snow Leopard is an added bonus. Stuff that we really don't need to complete a task.
This is why I don't like the idea of not using a disc. If you don't have wi-fi access, you are out of luck. Plus if your computer is running slow or if Apple's server is down... it will take you longer to repair or restore your computer.
btw I don't these Macbook Pro will be obsolete. I see a lot of Macheads still using Powerbook G3.