In the few short weeks that I have been playing live games, I have run into a moderate number of professional live small stakes players. I would estimate that I have had table time with 500-600 individuals and that between 20-25 of these individuals (there was actually 1 female, so I have to be gender neutral) were pros. I'm not counting the pros that I have seen at tables other than mine (particularly the higher stakes tables), nor am I counting the props (of which there are quite a few). I did not count the dealers who play during their time off (a couple of the dealers are great players, most are average).
That works out to about 4% of my opponents that were pros. I will actually chop this number down to 3% because I believe that many of these are wannabe pros only. I will discuss these individuals later.
I realize that my sample set is quite small so far. Unfortunately I do not have enough free time to collect as much data as quickly as I would like. :P To give an idea of the context, the poker room has roughly 20 poker tables. It is one of the larger poker rooms in a city of ~1 million, and the municipalities in a radius of 50 miles have a population of maybe 4 million. There are probably a half dozen sizable poker rooms in that 50 mile radius where poker has been legal for years. My table time has actually been about 65% $6/$12, 15% $8/$16, 20% $20/$40.
3% is a misleadingly low number because you must realize that a sizable percentage of the opponents leave the table within 5-60 minutes because they bust out of their chips (and possibly multiple rebuys). The (real) pros virtually never leave because they are broke. The majority of the time they are accumulating chips, have plenty of cash to rebuy (with the primary assumption that their chips were only depleted due to bad beats), or move to other softer games.
The reason I say that 3% is misleading is because you might think that with only 3% pros, you will only be playing with a pro from time to time and very rarely with 2-3 pros. However, this is not the case because these players are present for such a large number of hours per day. Those players might actually represent closer to 10% of the players (in the 6/12 and above limits) that are in the poker room at any given time.
To be fair, there are also a moderate number of non-pros that put in significant table time (e.g. retired people). However, I still stick to my statement that pros represent much more than 3% of the players at any given time.
I wonder how accurate my estimations are, and I also wonder how these ratios compare at larger limits, say 40/80 -> 80/160. I have no data whatsoever on games lower than 6/12. I can't see how any pro could net enough at limits lower than 6/12 to cover their nut.
I do not yet have a good estimate on how many BB/hour a great player could make in the 6/12, 8/16 limit games. My very loose guess would be 5BB/hour. However, I imagine that any "great" player would be playing at the higher limits, and would only be present at these limits when the higher limit games are tough or unavailable.
In regards to the subject of wannabe pros: They have some knowledge of the game, but definitely have large holes in their knowledge (don't know their odds, can't count their outs correctly, etc). They are all invariably young, almost all wear sunglasses while playing all the time (compared to many people who carry sunglasses, but are not always wearing them). I expect these types of players to break even or lose about 1BB per hour until they give up or go broke.