If you look at the Themes - Net Builders forum, you will notice is is completely full of Free WordPress themes from just a few authors.
The problem with this is that members who don't make too many themes, or want to sell individual themes will get their threads buried in a day when one of these 'power themers' will come along and post all of their promotions.
My suggestion is that if you are going to make a free theme, theme database, or something like that, you should just have one centralized thread where you can keep posting your new themes and information. This won't apply to people who post once in a while, just people who plan on constantly updating us with new themes.
This way, when I want to make a proxy theme once in a blue moon, my info thread won't go to page 4 because of a bunch of free WordPress themes