Cooperation in online shooter games

Almost all online first person shooter (FPS) games include some team based modes. Some only focus on that aspect, like Rainbow Six 3 or America's Army (a great, free-as-in-beer, army simulation game). But in reality, there is not that much collaboration, building strategy, covering each other,... going on in these games. Phil calls this problem the "cowboy factor" in Why multiplayer is a failure.

Here are some of the elements that contribute to this situation: anonymity (most of the time your team is formed of strangers, can you trust them to cover you?), communication limitations (how fast can you type when the enemy just threw a grenade), environment awareness (you don't see teammates unless they are in your narrow field of view), incentives (you can actually be successful running and shooting on your own), jerks, not to mention cheaters (that tamper with the software to obtain unfair advantage).

A number of these are technical limitations. I think they do contribute to the overall problem and I'm sure the situation will improve as the technology improves (wide view with 3 displays, headset microphone communication,...).
But the remaining ones really look like social software problems (see Shirky's "A Group Is Its Own Worst Enemy").
Suprisingly, I found very few articles discussing this design problem.

Many of the common design solutions suggested by Shirky are already being applied: have user identifiers, a reputation/reward system and a barrier to entry.
For example, in America's Army, the barrier is the training that you must pass in order to access certain maps or roles (sniper, medic).
The game also includes a reputation system, called Honor, which is based on your accumulated past scores. This score incorporates incentives for achieving goals, staying alive, killing enemies, taking leadership roles and avoiding friendly fire (based on Rules Of Engagement). Higher Honor scores allow you to access more restricted servers and increase your chances of getting assigned to the role you want.

These design choices certainly do help avoid some of the worst problems. AA even creates some cooperation and discipline in certain maps, like the Bridge Crossing (it's usually impossible if you just rush and the level design prevents players from dispersing and playing too solo).
Some more social behaviors also come into play, in the form of vote kicking (for campers, team killers,...) or the emergence of clans.

Yet all these factors don't really succeed at achieving team work. Gamezone still describes AA as "An Army of one, playing with a bunch of other Army of ones".

How to make the game fun and rewarding, while encouraging more strategic and tactical cooperation?

This reminds me of a great example of creative thinking applied to game design: KidTrade. One of the goals for that design is to help avoid the eBay effect (virtual goods and characters being sold or traded online), which is a problem often perceived as inevitable.
Can the same kind of out-of-the-box thinking be applied to solve this cooperation problem?

Some other online game genres like MMORPG games were able to foster more collaboration. It's not to say that they don't have other problems, but it's pretty common to join a team for the duration of a game. It may simply be because the game is impossible or boring to play solo, and some of the limitations that I mentioned earlier are not as bad (you have more time to type in a turn-based RPG and you have better awareness of your teammates and the environment in a third person view).
The question is how to create a similar effect, where strategy and teamwork provide a significant advantage (and thus incentive), in multiplayer shooter games.

I think Halo 2 did a pretty good job in this area; there are several clans who have practice and training sessions, the voice communication is just as efficient as voice communications in the real world, and for people for whom clans are too much, there are parties. I have seen some amazing examples of coordination, adapted team strategy over successive games, etc. Given respawns, playing Halo 2 is more like a football game than real combat, but coordination can get pretty sophisticated.