phloog said:3) the document is revocable, and
4) WOTC is clearly trying to move away from Open (insert your definition here) gaming
Personally, I think 3 & 4 are going to bite Wizards in the end more than they (or anyone else around here) thinks that they are. Some folks seem to be looking at this as Wizards trying to "crush" the open game idea - that's frankly impossible. It can't happen - it's too late. They can't put the genie back into the bottle and, what's more, when Ryan Dancey proposed the whole thing 10 years ago he KNEW that they'd never be able to put it back into the bottle. If they really think they can do it they're kidding themselves.
However - by making the GSL revocable what they ARE going to end up doing is fracturing the market far more than it currently is. There is a strong incentive for NOT switching your game line over to the new edition - because once you do you're at the mercy of Wizards decisions on edition releases. If you're making D&D adventures and campaign settings this is probably fine for the next five or so years - but I'd hate to have to make the call on whether or not to put out a new campaign setting when we start getting into "new edition" speculation territory, which will be anytime after the first five or so years unless Wizards specifically decides to share its new edition plans with the 3rd party publishers, and I tend to doubt that that will be coming on the horizon anytime soon.
And meanwhile there is now zero incentive to put your new game out using 4e mechanics. Some really good non-D&D games were spun off from 3e - Spycraft and Mutants and Masterminds both immediately come to mind. Regardless of what the d20 GSL looks like if it is revocable there is zero incentive for anyone to publish a new game with those mechanics - better to come up with your own mechanics so that you don't have to worry about revocation. Even sticking with OGL 3e mechanics loses its strong incentive - the reason to do that in the past was to maintain a certain level of compatibility with the current edition of D&D to draw on that pool of potential buyers. You may be able to do that to some extent by sticking with 3e OGL mechanics (the basic roll a d20 and add a number mechanic is still there, after all), but the level of compatibility is going to be less than it used to be, making the incentive much, much weaker than it is now.
And this is where Wizards is making, IMO, an error. Those games weren't stealing customers from Wizards - they were keeping customers playing D&D-like games. If your sessions are bouncing between d20-based games you're going to move back into regular D&D play pretty easily once the inevitable thirst for dungeon crawling rears its head again. If you've moved off to play a modern game in GURPS or Savage Worlds or some non-d20 system, you start to think about how you might do your fantasy game in those systems instead and now Wizards loses some customers for the longer term. This is what happened in the 90s when TSR was busily non-innovating and threatening to sue the pants off any fan website posting any D&D material - many of us started moving our fantasy campaigns to different systems because we were playing those systems more than we were D&D.
And sure, Mutants and Masterminds and Spycraft and other d20-based game systems will probably stay out there, but the less they are like the current edition of D&D the less "pull" they have on players to come back to D&D. Heck they might even encourage players to pull out their 3.5 edition books when they want a dungeon crawl instead of going 4e.
So personally that's where I think the error is - and who it's going to hurt the most. Wizards is going to get bit by this more than anyone else is because Wizards CAN'T fulfill all of the gaming needs of all players at all times. Under the old licensing scheme they could at least keep those players in a "D&D orbit" when they decided to shelve their D&D games and play something else. With this one they're not going to have that. Which ultimately may be good for innovation in the market for game mechanics, but is probably not the intent that Wizards has by "closing up" their license. Meanwhile I think most of the 3rd party companies will do fine with this licensing schema - provided they recognize that putting all of their eggs into the 4e basket probably isn't the best move unless they JUST want to be a 3rd party D&D publisher. Nothing wrong with that - there's obviously a market for it - but if you want to put out your own game lines you're going to want to keep your games as far from the 4e GSL as possible, I would think.