The 6-player max No Limit Hold'em tables have exploded in popularity at the major online poker rooms over the last year. I suspect that the reason is twofold. First and foremost, there is less waiting between playing your hands - and let's face it, we humans tend to be an impatient lot. Secondly, much looser play is warranted than in the full ring games. Those two aspects of short-handed action add up to playing a whole lot more hands. As poker players, this is really what we want to be doing anyway. So the popularity of these games should be no surprise.
But playing more hands is a sure way to quick losses, even when short-handed, if you don't go about it properly. Playing like a maniac just isn't going to get the job done. This is because it's just too easy (even for fairly weak players) to develop effective counter-strategies against maniacs. They are the easiest types of players to beat in No Limit, regardless of how many people are at the table. Selective aggression is still the winning approach, as with full tables, just with a much wider range of selection. Most important is playing a style that allows you to take many one-try stabs at small to medium-size pots.
By one-try stabs, I mean that you need to know how to let go of a pot that you are trying to win on the flop if you are called. This is critical. If you can't do it, don't expect to win much in short-handed No Limit cash games. All your accumulated profits will leave your stack in one fell swoop and go to the shark who smooth-called you on the flop. Your next bet will have to be quite large if you plan on continuing with the aggression, and that's when you can expect the shark to raise. When you get called on the flop, just let it go.
The style you need to play in these games is a raise or fold philosophy, especially before the flop. If nobody has entered the pot yet I will raise with any two cards 7 or higher most of the time. If somebody else has entered the pot ahead of me, I won't play anything except super-premium hands, period. You have no business in any pot where you are not the aggressor, barring a rare exception. In fact, I insist on both "power and position" if I am going to see a flop. Power meaning that I am the last pre-flop raiser, and position meaning that I am last to act. On the flop I always bet around 75% of the pot no matter what cards hit the board. Always. If I meet any kind of resistance at all, including a call on the flop, I simply give it up (unless I happen to be holding the World's Fair, which does happen sometimes).
Here is what is going to happen if you play this way: 1) You will steal a lot of blinds, 2) Almost every flop you see will be heads-up or three-way, 3) You will win the overwhelming majority of pots on the flop, 4) The pots you don't win on the flop will be way more than made up for by all the ones you do win, and 5) The rare occasions where you flop a monster against a decent hand will get paid off big-time. You will be the dominate force in your game, and your flustered opponents will watch helplessly as their chips continue to desert them into your stack.
You see, they just can't call that flop bet. Play this way for a while and you'll start to get it. If you occasionally screw up and find yourself on the flop when you are not the aggressor, you will curse yourself for being there playing like a fish, because you won't be able to call that flop bet either. It's like the great San Francisco 49er offense of the late 90's with Steve Young at quarterback, coming at you with those slant plays. The defense knows exactly what's coming, but they still can't stop it.