For me its profitable. I can play an average of about 3 hours a day, and make about $100 a month playing mostly SnGs and MTTs. now I never play for more then $5 online, or $100 live. With that said, I could be up $200 during the week, and lose $100 live. or hit for $500 one month, and blank for the next 2....
I would suggest really learning the game you want to be good at. Without saying "you can know everything" there will come a point when you realize there isn't much more you can learn. When that happens, it comes down to how you handle variance, and the evolution of the game.