Now that I have the correct Serial number. I read the EULA and you're right, you can have it on 2 machines as long as you own them and you don't use both machines at the same time.
By the way, Adobe originally gave me a windows serial number. Somewhere it makes a difference. I wonder why they assumed I had a windows machine when I had given them a .mac email address?
It would then also show a failure on the return form since it doesn't ask the user what machine they use.