I didn't buy the upgrade to a gig of ram yet, and well I'm content with the memory situation I have now. I'll buy another 512 MB (perhaps 1 GB!!!) stick to upgrade my memory situation at some later time.
There's an app out there called "Do I Need More Memory" and it may provide some insight on how much memory you need. I'll be happy to e-mail you the app if you are unable to find it online (I forgot the website)
Considering you can get 512 MB sticks of RAM for your powerbook for around $100 now, I'd say it's a good idea to add more memory.