To date 7280 people have linked their Google+ accounts to Twitter using our service. We check these accounts for new Public posts every 10 minutes which represents a significant number of data points
If anyone thinks this is in anyway indicitive of Google+ usage they are fooling themselves.
Google has deliberately tried to build Google+ as a standalone product (as opposed to Buzz, which encouraged Twitter etc integration). That's a much slower path to take, but from what I see (in terms of in-depth conversations on Google+ itself) it's being quite successful.
Sure but if overall users and usage increases, I'd still expect that rate of increase to be higher than the rate that people learn to stop publicly sharing things. So if public shares are decreasing, it seems likely that overall usage is stagnating or decreasing as well.