If you click on the "about us" link at the bottom, it leads to a page which has some statistics on the bottom. Currently it says that there are 77,591 published hubbers.
You could also try to estimate by the directory: http://hubpages.com/directory/ which has 252 pages with 201 names per page. That translates to 50,652 users. I obviously didn't count each page, so that might be off by a bit.
As for active, I don't know if there is any information on that. If one wanted to, I suppose someone could take a random sampling from the directory and use that as an estimate for overall activity.
I randomly picked 10 users and only two of them had more than 10 hubs or followers. That is a very rough estimate, but I wouldn't be surprised if somewhat active is around 10-20% and active around 5-10%. A more detailed estimate would actually make a pretty interesting hub, though, I'm not sure that Hubpages would want someone to do that.