No, Google does not recycle email addresses.
Google...has confirmed to Webwereld that it does not recycle unused accounts. Users can delete their accounts, but this "won't free up your username. Once you delete your Gmail address, you won't be able to use that same username (firstname.lastname@example.org) in the future," Google says on its site.
Yahoo! Mail does, however, delete inactive email accounts and makes the usernames available for new people. However, they claim that they have ways to keep people from using this to impersonate the previous account holders. For instance, they have an agreement with Facebook to prevent a newly-acquired address from being able to access an older Facebook account.
That said, deleted accounts are not available right away and any of the email messages that you'd deleted would still be long gone. The real risk is of future email messages meant for you being sent to someone else.