My tip is, if your not 100% sure on what you are ordering and you feel you might have a change of heart on what you are purchasing, stay away from Google Checkout.
Reason why is Google checkout will take the full amount instantly from your bank/credit account and hold on to it. Then it can take up to 5 days after the date of cancelation, It can be less depending on your bank.
Even worse is Google Checkout do not have a telephone support line, everything is done by email, and you can expect to be given a ton of automated crap and are never sure if you are actually typing to human or a bunch of auto responce macro gibberish. If your lucky enough to get in contact with someone in google checkout that has a pulse it is still all on luck if they are able to help you get a speedier return on your refund.
If your certain that you won't be having second thoughts, however I have found them to be decent but in many ways what you get in speedier payment/checkout you lose in flexability, such as editing an order or making amendments before your order dispatches, when if you pay direct you still have that flexabillity with most places as long as your order has not been dispatched already.