I have routinely cleared the cookies and blocked most of them every time I was logging. I also routinely ran the ATF Cleaner and Did AdAware scans. I was also protected by regularly updated Symantec Antivirus and Firewall, which I ran in place of the Windows Firewall.
How vulnerable could I be to personal data being exposed or otherwise compromised if I give the old machine away? Also is there an easy way to transfer the license for the software to a new owner, so all updates are no longer registered to me (change the name associated with the computer)?