Supports a smaller number of countries for payments than Paypal, very few countries can be account holders who take money (eg: you can pay via GC from Sweden, but you can't be Swedish and take money via Google Checkout) and Google don't have a history of customer service, do they? :p

I've actually had worse customer support with GC (who froze our account with 30k with no support phone line to call) than Paypal (their phone lines are up until 11pm PT).