If you try using Google Base to take payments from customers, let me (and my readers) know how well it works.
It seems improbably that Google Base will take any users away from PayPal which is so standard now. At least, it will take a long time to make a dent, unless somehow the user experience is better with Google Base.
(I personally have had tons of usability problems with PayPal. I only use it rarely, and I always seem to have problems with passwords and with the data entry screens. If Google Base uses the same login as most of my other features, then that might endear me to them.)
So let me know if you try it out.