1) Go to recipient computer
2) Delete said email
3) ...
4) Profit?
not really, unless u can hack the gmail servers. by which time it's already on the recipient's incoming mail server if not already in their inbox
that being said, i found even within a corporate messaging environment the unsend/recall function does not work. you can send out an email internally, and immediately recall it, but to the recipient, they will see 2 pieces in the mailbox even AFTER you have unsent it, one with the original msg, then a notification that the sender has attempted to recall it. maybe it's a bad exchange server setup?