I played a lot of online poker when it was allowed. It is still allowed in many countries, but here in France, the taxes are so high (lol at a tax/pot) that you cannot beat the house+the government, so there is very little point in playing.
The level was better, but you could play more tables. You ended up playing like a robot (I played 4 to 6 tables at once. One of my friends played up to 12).
Actually, I was a semi pro. I tried to play part time poker and use the second half working on my game (it was another one at this time), but getting enough cash/month playing poker took so much time and energy that I didn't get much progress done on my game.
The level of the average player is also much higher than it used too, and now that it is botable, it might be even harder to get any serious money out of online poker that it used to be, so I would not recommend it (at least, that is what my friends who are still playing tell me).
I also played in casino which was a much nicer experience as you could have conversation, but it was also weird to have direct contact with people you were trying to get money from. The rake and taxes are higher but the playing field is so bad that it is still more profitable now IMO.
It used to be around 5% when I played. 3% with rakebacK. It is now 7% after tax, and 4.5% with rakeback.
It is a huge difference, as you lose the money on every pot you win, so it can quickly reach 50% or more of your winnings as your edge is usually not that high.
Being taxed on the overal profit would have made much more sense, but the French government only saw it as a big cash cow, and never thought about the implications that taxes would have over the number of players.
I don't play anymore (I kind of burnt out), except sometimes with friends. It is critical to bet money to avoid everyone playing like donkeys. Even a tiny cash prize (if playing tournaments) or stack size (if playing cash game) would do. We had a stack size of 2$ when playing together (we used to play with a stack size of 100-200$ online or live, so it was only to make sure people where not doing dumb things to unwind).
Regarding strategies, the most important part is knowing how to mix up your game: how to leverage your reputation to maximize gain.
Wheter you are loose (play a lot of hands) or tight (the reverse!), you also need to be agressive, and bet/raise much more than you call (folding is ok of course!).
Paying to see the cards is usually a losing proposition.
Also, discipline is king. Don't believe the small voice telling you that "it will be ok, at worst, you'll see the cards and improve" when you have a strong suspicion you are beaten.
And when evaluating your strategy, don't take into account the data you could not suspect (ie, if you managed to win because you lucked out a 1:5 draw, don't consider it a good play, and try to make sure it does not happen in the future).
I played a lot @Full Tilt (which has been bought by Pokerstars since).