Very expensive with wimpy output compared to tungsten or fluoro. They are cool but I am waiting a few years for them to reduce price by at least half and double or triple output. Also, Barry Green reports that at least on the larger Litepanels, a noticeable shift in color when dimmed. I have used the smaller ones bit I did not dim it so I cannot comment on if the smaller Litepanels have the same color shift.
Have you looked at the VidLEDs? Not nearly as cool as the Litepanels but so much more affordable.
Just to echo Dan's response, the LitePanels are very sexy. I've rented the Full 2 light kit twice and I'm always excited to use them and love the portability, but I'm always disappointed at their output. I had the kit for a week while shooting a bunch of interviews, but was only able to use it twice.
Don't get me wrong, LED is the future. They're 2x-5x more efficient than florencents, but we're a couple of generations away from a unit that will fill the bill.
BUT, I'm shooting DVCPRO with no gain, so the camera likes a lot of light. If I was shooting with a Pany, Canon, or Sony Prosumer line with a 6db gain, the LitePanels would give a lot more punch.