You've probably already heard by now, but the 4e GSL and accompanying SRD is now out. You've probably already heard because Trollsmyth, the Chatty DM, and James Maliszewski are already discussing it. I mention it for completeness, and because it's worth checking each of those sites for their own take.
None of the reactions are good. You can't reproduce Monster Manual stat blocks in adventures, there's some dodginess about web support, if you Wizards publishes something similar to what you're already doing you have to cease-and-desist immediately, no questions asked.
A lot of it sounds like they're trying to avoid competition with their D&DI, which kind of worries me because at this point I have no confidence that the thing will actually be usable. I hope it will be, but if it ends up disappearing I'd like to be able to access fan-created resources that do similar things.
What I don't really get is why they appear to be so worried about people taking their system and doing other things with it, stuff like Iron Heroes and Mutants & Masterminds and so on. I could be misinterpreting it, but it looks pretty much impossible to do that with the new license.
That isn't going to keep people from jumping ship to other systems, it just means that 3.5/d20, rather than the new edition, is going to be the keystone system that people learn because they want to be able to play a bunch of games with one set of rules. And people who care about that kind of thing may well be inclined to pick up Pathfinder as their fantasy RPG of choice.
But I'm not much for prediction or for business, so there's a good chance I'm completely wrong. I'm just disappointed that it looks like there won't be nearly as many supplements for my game, especially the crazier ones. I wasn't planning on dropping 3.5 completely anyway, so this is just one more reason. And I am starting to worry a bit about the fan site policy, but that's a wait-and-see situation, too.