Just some news to pass on, today. A number of deviantART users have found that art4love.com has been selling their work as prints without their permission. I'm not sure how many artists the site has been ripping off, but in my personal experience, I've noticed that a lot of art thieves tend to be very prolific.
Keep in mind that the site seems a bit wonky. You'll probably have to replace "art4love.com" in any URLs with "http://188.8.131.52"
So, my first recommendation is that everyone who has a deviantART account (or possibly any other art community) check out the site and look for their work. If you find anything of yours, take a screencap with date and time. Print it, if possible, with a date. This could be important later, if you need to go to court.
My second recommendation is that while doing so, you keep an eye out for any familiar pieces. If you see a piece that you recognize, it's best to contact the artist with a link and let them know. Screencaps with dates are a good idea here, too.
This news post on deviantART sums up a number of good ways to take action on this issue.
Lastly, if your work has been ripped off by this site--or any other site--remember that you have rights as an artist. Check up on copyright laws and how to write a "Cease & Desist" letter.