Powerbook Memory

Right now, I have 768 MB DDR SDRAM on my Powerbook G4

I want to upgrade but have a couple questions:
a) Is it worth getting more Memory, with only a 1Ghz processor?
b) How much should I get?
c) Is it worth buying it on ebay?

Canadaram (google it).  I think I have a coupon for $10 off. 

RAM is the cheapest upgrade, and if you’re thinking of running 10.5, you’ll want more.

I doubled the RAM in my Macbook from 1gig to 2gigs, and it almost quadrupled Photoshop performance, especially with large files.

<3 MiG