That is a great question, and I wish I had kept better track. I've been playing for about 15 years now, and can say that only the last 6 have been profitable (at least on a somewhat consistent basis). Most of my early experience was in live limit-games, and I should have kept better records. You would see the occasional player at a table with a notebook keeping track of hands he was playing, or even just results from sessions, but sadly, I didn't understand the value of introspection. The internet has changed my game, including giving me tools to evaluate my play, and has forced me to be more honest with my results.
Since moving online, I have changed to mostly NL HE Tourneys, but I do still enjoy $1-2 NL cash games when I can find a live one. I don't play ring-games often on the net, since I feel I have a better edge when I can read a live player; and it is a lot easier to guess if two players are working together when you can see them in person. (It also gives me a reason to go to Vegas every once in a while
Online play and access to great info in places like Cardschat has definitely sharpened my play, but I do miss the rush of walking out of a back-room game with a 'gangster-roll' of hundred dollar bills after a good night.