Not sure if it applies to you steam buyers, but there is a shortcut in the GTAIV folder from my retail version that is titled 'revoke activation'.
I have it on Steam and it doesn't seem to be there. I wonder if the /revoke still works anyway.
Why the need for it I wonder, when I thought there was no limit on activations?
I've got my files but when I copy them into saved game it just starts from the first mission
If you did you'd generally uninstall stuff which you wanted to use again yourself, whether it required online activation or not.