That means it will be limited to 24hz or 30hz gaming at 1080p. You see, HDMI cannot input enough information for more than 60hz at 1080p. 30hz per eye with 3D. The 240hz means that it will interweave extra frames between the normal inputed frames, but this will cause latency with gaming, and will result in it sticking with the maximum 60 frames per second limitation of HDMI at 1080p which is 30hz per eye, but 30hz is not a normal valid refresh rate, so it will likely be at 24hz.
It does work. I have that set up and have tried the monitor with a GTX 550 TI, a GTX 580 and a GTX 680. In 720P it worked with all content I tried.
In 1080P it seemed to work for some content and not for others with no reason I could detect.
In terms of quality, it worked as well as it did for the playstation 3. In my opinion, no much better or worse than any other 3D monitor I've used. None seem that great because they are too small to be really engaging despite the advertizing.
My advice for anyone looking for a great 3D experience for gaming would be to get one of those Optoma 3D gaming projectors for $800 new or $400 used.