One of the fascinating things about the Open Game License Wizards of the Coast introduced with the release of Dungeons & Dragons 3e back in 2000 is that it more or less guarantees that that that particular edition of D&D could legally remain in print forever. Indeed, Paizo's Pathfinder RPG is more or less just that -- 3e under a different name. Except for its trademarked name and a very small amount of IP (mostly iconic monsters, such as the mind flayer and beholder), any publisher can produce their own version of Dungeons & Dragons without having to ask WotC's permission or pay them one red cent for the privilege of doing so.
This is an entirely new situation. Neither 1e nor 2e, let alone OD&D or its descendants, was ever made open content and so, when a new edition was released, the previous edition effectively "died," which is to say, it had no legally permissible commercial support. Fans of those older editions had no choice but create their own material to share amongst themselves, which they did, often with great gusto. Still, I think it's fair to say that, especially in the days before the ubiquity of the Internet, it was very hard to recruit new players to an older edition of D&D once that edition went out of print. Thanks to the OGL, though, that need never be the case with 3e, provided someone is willing to publish it.
Interestingly, it also need never be the case with older editions either. One of the fascinating and unexpected twists of the opening up of 3e is that, because this edition, while different from previous editions, is nevertheless derived from them, enterprising people have been able to use 3e as the back door through which to retro-engineer early versions of the game, most notably the Moldvay/Cook Basic/Expert edition (in two distinct flavors) and 1e. (Perhaps unsurprisingly, no one has yet done this for 2e)
The whole reason why these "retro-clone" editions are possible is because the OGL basically amounted to WotC's admission that game mechanics are not copyrightable. This is pretty well established in law, as I understand it, but that never stopped TSR from legal bullying against third party publishers who tried to make a buck off of D&D by producing compatible products back in the day. WotC hoped that, by bringing third parties "inside the tent," so to speak, they could ensure better quality, greater compatibility, and -- perhaps most importantly -- feed sales of official D&D products.
Exactly how well the OGL succeeded on any of these points is a matter of some debate even eight years later, but it's clear that the most lasting effect of the OGL has been to inspire others to try and recreate retr0-clones of other beloved games from the 70s and 80s. I can't even begin to list all the ones I've encountered, but the ones of most interest to me are Mutant Future (a Gamma World clone) and DoubleZero (a James Bond 007 clone). I have no idea how Gary Gygax felt about OSRIC, but I do know that David "Zeb" Cook approves of the retro-clone of his Conan RPG, known as ZeFRS. James Ward, creator of Gamma World, has publicly spoken out against retro-clones, which he considers theft. I'm not sure that his position has much merit either philosophically or legally, but it's still fascinating to note that there's still a difference of opinion regarding the nature of these games.
As for me, I'm generally in favor of retro-cloning, if only because it theoretically ensures that the great RPGs of the past are not lost to future generations because some megacorporation has locked the rights away in a vault somewhere "just in case" they can squeeze some more money out of them at some future date. I'm increasingly of the opinion that the future of this hobby depends ever more on us than it does on game companies, some of whom have sadly turned RPGs into IP mines for novels and video games rather than into "products of your imagination," as the old TSR ads used to proclaim. I'm a big believer in do-it-yourself-ism and the retro-clone movement is all about that. I can't help but admire these guys for what they're doing, because they're quite literally preserving both the past and the future of our hobby.