Personally, I think e-mail is the best way to get responses regarding your site. I found that those that are willing to send an e-mail about your site will be more likely to point out any problems in more detail than those on a forum or tag-board.
I received more feedback via e-mail than through my site's forum, so I ended up taking the forum down. Almost everyone that surfs the Internet uses e-mail, but not everyone likes to sign up to forums or post in a tag-board where everyone can see your IP number (JKaizer needs to fix that on his tag-board, for example).