I would say that in a strokeplay situation ( whick is extremely rare) - at least 80% of private club golfers could not play to their handicap on a regular basis.
That's the way it SHOULD be. Since the handicap is 0.96* the Best 10 of your Last 20 scores, no one can "play to their handicap regularly". They aren't supposed to! In fact ~24% percent of scores should play to their handicap. (0.96 * 0.5 * 0.5 = 0.24: 0.96 * the average of the best half of one's scores)
For example, Sunday was fine whether at my club. We had 23 guys in the Sunday morning game (we play a stableford game, no gimmies, all rules, and as far as I know, everyone plays by the rules cause you're going to catch hell if you don't). Handicaps for our Sat/Sun morning game are only established using scores from other Sat/Sun morning games. So there is no sandbagging / vanities handicaps in the group since all scores for handicapping were produced within the group. And you always play with different guys each week.
Results are online
http://www.northshoregg.com/scoreboard/showcal.php?year=2008&display=1This Sunday only 2 of 23 players were net below par. The handicaps were +2 1 3 4 4 5 6 6 6 7 7 10 10 11 11 11 14 16 16 17 19 21 22 and the 6 and the 21 broke par (the course rating is 71.5 and the par 72, so it's a far comparison.
Since April (20 weekend rounds/games) 125 of 518 rounds were net under par. So precisely as expected (the handicap is approximately the average of your best half of rounds) we saw 24% of guys beat their handicaps over a 10 week period.
I shot a (rare) net 72 Sunday (88 off my 16). But just this year I've been as bad as 110 at 14 for a net 96! Was I a vanity handicap the day I shot 110? Was I a sandbagger when I shot 87? Or am I like most 16 handicaps and have wild differences in my score depending on if I can keep my driver in play?
The only way to play to your handicap "regularly" is if you have very very low variability in your scores.
And who cares about vanity handicaps. The only time I dislike vanities handicaps is when the guy can't pay his bet.