Thanks guys
Thing is how do you change it for every transaction? If a site is paying you a few times a week say... You have logged an address just for that site. How would you change it for each tx? Keep going back to the site daily and entering in a new address? Impossible to do it you had many of these sites paying you?
In such a situation you don't change the address. Simples.
In future we might see solutions to these scenarios as well. There are three competing implementations that I know of:
1. Deterministic wallets. You submit the master public key of a branch and a the site generates a new address for each transaction using that.
2. Bitcoin payments protocol.
3. Stealth addresses.
Only time will tell which one of these gets the widest adoption.