My girlfriend and I have been riding Freelines since late 2006. A little hard to learn but super fun once you do! Their portablility makes them a great choice when I don't feel like hauling around my longboard. Downhill is where these really shine! Kinda sketch at first, but once you're comfortble on them you can carve like a snowboard and even slide(frontside and backside)!
There are thousands of Freeline vids on youtube. Flatland riding and tricks are the most popular but there are downhill and vert/park vids as well. To see the best US Pro Rider, search Mattie Tyce.