i am worried i will be charged extra for buying games because i am in england which uses £ but this site uses $. is there some kind of transaction fee? i use Barclays if that helps
thanks

Ouch, that's around $8. It's definitely without a doubt the bank's fault. GOG already bundled the VAT and all those fancy charges with the game, so there's no excuse for them to charge you again.

In my case, and you can tell that to everyone here as an official GOG.com statement, my credit card got charged exactly 9.99 when i bought some titles here, not 1 cent more. : )

Yes you can. Enter it when you link your card, and you're set.

My bank charges a 1.75% exchange fee when I pay in foreign currencies using my Visa debit card. Check with your bank or credit card company!

You could always use paypal.

You'd have to check your credit card company to be sure, but being Canadian I quite regularly buy things in USD (for example my current monthly subscription to City of Heroes) and on my Visa statement it simply shows the price in USD and the exchange rate at the time of purchase (Visa's rate, which is a bit more than the actual exchange rate at the time but still reasonable), then gives the total in CAD.
To use my City of Heroes subscription as an example it's $14.99usd, and one month it ended up costing $19.11cad while another month is cost $19.42cad. Back when the Canadian dollar was on par with the US dollar the payment was around $15cad.