To get true aliases while using the Gmail interface, you actually need to have your own domain and use Google Apps. There you can have 'nicknames' (Google's word for aliases) that are easily made and deleted.
But I
believe I heard someone say once that they successfully used the Gmail "alias" feature (using the "+") with some online service (Craig's List ?). The automated system sent mail to the username+whatever@gmail address, but the main address never got spammed -- or at least not yet.
