As a minifigure collector, this seemed perfect to me so I signed up (quick and easy) and then give the site a once over. After updating your want list and your have list (a fairly lengthy process but you only need to do it once), all you need to do is push a button and have Swapfig find a bunch of potential trading partners for you. The potential matches will all want at least one minifigure from your "for trade" list and have at least one minifigure from your "want list" which is awesome.
For your first trade, you must do a one-for-one swap. I ended up sending a trade proposal out where I offered my Disney Minifigure of Peter Pan in exchange for a Series 15 Frightening Knight minifigure. Since I was a brand new user, the person that agreed to my trade made me send first (which seemed fair to me). After he received his end of the deal, he mailed off my minifigure.
In about a week's time (give or take a couple of days), I reduced my extra minifigure pile by one and reduced my want list by one! I'm also within two minifigures of completing Series 15 finally...only the Tribal Woman and Jewel Thief still elude me!
Overall, I found Swapfig very easy to use (though the website itself has been down for maintenance quite often lately). I am hopeful that the site grows in terms of number of users because I have yet to have anyone offer me a trade (I've been on the site for a couple of weeks of course). From my initial experience, I can recommend Swapfig to other minifigure collectors out there!
If you'd like to check out my collection on Swapfig...and perhaps even make a trade with me, here's a link to my profile page. I hope to add even more of my extra minifigures to my page in the future...but for now I have a decent selection of extras that I'm looking to trade away!