Yeah, I keep offering to test if someone would buy me a 360, RB3, and sponsor me. Strangely, it hasn't happened ;)
But yes, it's mostly watching, with some occasional playing. I know my biggest problem would be testing pro keys, as I really don't know what I'm doing there, but I could test everything else. It doesn't require you to be awesome, just good enough to understand how things should generally be charted.