I have several addresses and I never hit the "new" button on the client. I am planning on opening some merchant services and I can't have it changing like this all the time. Will it still send to my old addresses??
The client automatically generates a new address when you receive a payment on your 'old' address - this is to promote the use of a new address for every transaction.
All your old addresses are still in your wallet and will still 'receive' bitcoins sent to them.