High guys, thanks for the kind words.
You can all put your stuff in your signature, however we have a rel=nofollow on all links unless it's lifted.
There's more about advertising here.
Advertising on Tree World
Bandwidth. We get around 10gig of downloads and 7500 visitors a month, around 2500 new visitors a month and growing.
What you have to realize is that links back to your home sites help your site out regardless of anyone seeing your ad, it's part of the way search engines assess sites.