This could potentially be solved by using alias emails instead of just adding a tag to your normal e-mail address. I can imagine gmail offering a quick "generate alias" button that creates a EkTG522f3fhgtfh@gmail.com address that instantly forwards to your real address. Obviously you can delete this alias if you find that you are being spammed.
Perhaps someone here has some statistics to share? It would be interesting to know how common this trick is :)
[Edit: Better wording]