I couldn't help but notice that most of the responses to the question posed above mentioned handicapping ability as a factor, but did not speak to the more important question of betting ability.
Back in the day I was friends with this guy who was a top-notch handicapper. He could dope out the most impossible-looking pace scenarios, he had a steel trap of a memory, he could rattle off the most obscure statistics imaginable.
And he was a horrific loser. In fact, for almost a year, things were so bad he lived in his car. It was always my feeling that, deep down, for a variety of reasons I won't bore you with here, he WANTED to lose.
The person who has taught me the most about this game (a close friend's father) is a fairly unsophisticated handicapper. He doesn't use sheets, figs, or any other sort of numbers. Yet, since I've been tagging along with him, since Saratoga way back in '88, he has had ONE losing season. One.
Methods to his madness ? He doesn't bet between Breeder's Cup and May or June, at which time he bets Belmont (and Belmont only) once or twice a week and watches the NYRA replays every day to look for any trends, biases, bad trips, etc. He bets very few races; he bets only certain kinds of races (grass allowances and dirt claiming sprints). He concentrates almost all of his play on Saratoga. He keeps close records of his wagers.
Mostly, tho, it really comes down to his psychology. He trusts his conclusions, he doesn't give a @!#$ what other people think, he doesn't make the sort of impulse plays that eat away at his bankroll, and he bets with impunity.
So, yeah, I guess you can show a profit at this. It just takes a lot of discipline and the right mentality - two things that are not easily come by, I guess.