I'll just add to the online poker discussion since I played a LOT as well (though never for a living) and am now reduced to playing live, which I've been doing a lot recently.
I'm not sure how much collusion really went on. It turns out that a LOT of people were making a decent living (70-150K) playing stakes as low as 1/2 grinding multiple tables, and if any collusion was going on it was probably a lot higher stakes than that. The sites were definitely on the lookout for that kind of thing, and there were also sites like pokertableratings (much reviled by good players for a number of reasons I won't go into here) that captured hand histories and make them public so the general population had an eye into what was going on as well (they were not a philanthropic organization, but it did allow for people to examine closely players they thought were winning outside of an established winrate).
Winrates at onoline hold em are MUCH smaller than live, so the only way to make big money is to play a TON of hands (or play higher stakes). If someone is making an abnormally large winrate, people will know and they will be scrutinized.
One of the more intersting problems in poker (and this happens in all games, online and not) is what happens when the games get really tough like they were online (and still are, as far as I know). You end up with 5 players at a table who are very good and know who the other four players are that are good, and one bad player who basically is the reason the game goes. These good players aren't going to play very hard against each other because they know they don't have much of an edge- if you play 100,000 hands against an equally good player you'll both come out losers because you are essentially trading money back and forth with the poker site taking a cut out of every pot.
The pratical implication of this is, unless the bad player (The "fish") is in the pot, the good players (sharks) aren't going to bother, and they aren't going to play that hard against one another. This looks a LOT like collusion, and even though they tehnically aren't, when people get out of the way of each other and target a single player, that looks (and behaves) a heck of a lot like collusion. True they aren't seeing each other's cards, but the reality is they don't really need to. They have a good idea of where each other player is at and where the money is.
I've actually been enjoying playing live quite a bit more than online (the games are much, MUCH softer), but when you run bad you can lose a lot fast (which has happened to me over the last three months). I also struggle a lot with playing 30 hand per hour when I've played several hundred per hour in the past. It takes some getting used to