What do you know about this gate way and what are the pro and cons vs Paypal?
Google Checkout merchants must be in the US or the UK!
Google Checkout offers 2 main advantages - it gets you a great button on any adwords ad and it supports people who use the system.
The disadvantages are all set aside when you consider the conversion lift as a secondary system. If it's your only system you're a bit of an oddball... most sites either offer a direct credit card payment or paypal + google checkout. Google's system has some adoption, lots of recognition but very little usage compared to Paypal and Direct credit card payments.
I recommend offering a variety of payment gateways (if you can) as then people can pick the method of payment they prefer...
PayPal = Integration (Positive), Flexibility (Positive), Cart Support (Positive), Recognition (Positive), Dispute handling (Negative).
Google = Integration (Average), Flexibility (Positive), Cart Support (Positive), Recognition (Average), Dispute handling (Average).
Amazon = Integration (Average), Flexibility (Average), Cart Support (Average), Recognition (Average), Dispute handling (Positive).
PayPal is well recognised, highly supported, has the best API of them all but unfortunately their pretty bad in cases of payment disputes.
Google is pretty good on the recognition, cart support, and dispute handling support but their API isn't nearly as good as PayPal's.
Amazon are the best for handling disputes with payments but their pretty average in most other respects, the flexibility included.