One of the reasons I'm against a rating system is that, like every request, it requires developer time. If it was really needed, maybe players/GMs could use the existing Activity page of roll20 profiles to post comments? If I was to click the name of a poster and see a slew of flattering and appreciative comments from players, I'd feel more comfortable joining. It also has the benefits of: more detail than a categorical rating system, and allows you to see responses from both sides (such as, "Why didn't you show up last night?" "Sorry, there was a hurricane. My computer was thrown violently from an open window.")
We could implement the Activity Check system immediately, but should let all players/GMs we run into know to comment on each other's profiles to help create a better community (otherwise, 90% of the community would probably not know to start using the activity page). Things like Ajax's one shots would be a perfect way for new players to start building their status in the community.