I think that falls pretty well in line with what I've read about the user-contributed content phenomena: maybe 5% actually contribute content, a few more may edit, tag, or rate it, and the rest are just consumers. It seems like a very low number to start with, but it generally seems to work -- as it sounds like it did in your case. Although I also understand what you mean about visitors and professionals being "ready" for this new media.. Hard to say, but hopefully we'll learn more at the conference!

Nate