I think it's only fair. Most things cost a small fee when you use em to make money(ebay, paypal). It might be a complicated thing to get going but would be a good thing for the site. Could be something small like 2.5% - 5%. I've seen people donate after making money so it'd pretty much be the same thing. There's a lot of people that join only to make money and don't have any real desire to contribute to the site, only looking to make some cash. Just something I was thinking about while seeing all the different paid services going on right now. 2.5% of everything that they are making going back into the site would add up. could help and lead to better things down the road as the site grows even more.