Not sure about the demo but I still see plenty of people on my friend list playing the full game online and last time I played a few weeks ago it was still very busy. Actually, typing that makes me want to have a go when I get home this evening.
Probably doesn't help that it came out a while after the game when most people who were bothered about it had already bought it
Yeah as a lot of pople either had or still have the main game, the demo isnt much use. I still enjoy playing GRAW online, mostly with Krono and Ceeg nowadays.