I bought one as an experiment, mine is a Hauppage model. It came with a tiny little antenna. I picked up a lot of channels in my area, but strangely the foreign language channels came in real well but the main channels did not. Apparently I need a better antenna. My next experiment when I get around to it is to connect my tv cable to it and try it that way.
I tried mine with the software it came with and Windows XP, and also with Win7 by itself. It seemed to work OK both ways.
I had visions of using it with my laptop when I travel, but in many areas reception might be a problem. Connected to my TV cable I could use it as a PVR, and also capture screenshots. I might be able to store various programs on DVD.