This is fundamentally a good thing, I think. Anything that gets players thinking and planning during turns other than their own is great for maintaining group intensity and momentum. The dynamic of increased co-operation has made me pay more attention to D&D as a team activity - like a sport, but with dice.
Of course, most sports have an opposing team (in this case, the monsters), and a referee. Now, it's not common in sports to have the Ref controlling the other team, for reasons that I think are pretty obvious. In DnD the Ref does control the other team, and this can be a hard thing for DM's, especially newer ones, to balance. Is it competitive, or communal? Are you trying to kill them, or just make their lives hard enough to be fun?
Most experienced DM's and players can answer this easily enough, but it's a balance that every DM has to find for his/her own group. Ultimately, though, the role of the GM as Referee is a critical one, and one that I find very interesting, particularly because of my experience with organized sports (soccer and basketball, particularly).
I've had to deal with a lot of referees, and there are a lot of bad ones out there. It's tough to really categorize what makes a bad ref - it's like porn. Hard to describe, but I know it when I see it. Good ref's, though, come in 2 flavours; consistent and fair. As a ref, the job is to know the rules, apply them to a situation, and enforce them. Consistent refs decide on a rule interpretation and stick with it. You may not agree with the interpretation, but at least you know what to expect in a given situation.
A fair ref tries to make the game equitable, but often does this at the expense of consistency. Know you made a mistake on the previous rule call? Make a fudge for the player who lost out on the previous call. This sort of ref is less interested in pure rule enforcement than they are in a level playing field.
Interestingly, Wayward Mind over at Behind the Screens just wrote a piece on the "Friend or Foe DM" which I think dovetails nicely into my thoughts on this:
It's dealing with a different aspect of the DM role (how many hats does the DM wear, again?), but some of the priciples apply. If you are a Friend DM, you will naturally move to the Fair rule enforcement style. Players like things to be equitable, and a success-oriented DM will generally move in that direction.
If you are a Foe DM, though, I think you have a responsibility to be a Consistent rule-enforcer. Players will have difficult time with an antagonistic DM who is also less than even-handed about rule enforcement. Some players will put up with a DM whose villains and monsters are fundamentally nasty, seeing it as a challenge, but if they perceive that the same DM is tilting the odds in favor of those monsters and villains... Watch out.
Ultimately, of course, each group and DM will fall somewhere along the spectrum. The trick is to look for that sweet spot where most players are happy most of the time. If players are constantly insisting that they want a "formal house rule" or saying "the rule states", consider heading down the Consistent road. If you get more discussion like "we made a mistake in the last session about saving throws, so can I get that healing surge back", then you're working with someone who values Fair a bit more.