I'm an attorney. (See the user name I gave myself nearly ten years ago when I was young and still impressed with myself for making it through law school.) Though not an IP attorney by practice, I do consider it a bit of a hobby.
There are a number of issues that this thread brings up I'd like to comment on.
The Games & Law article posted by DMMcCoy was interesting, but it glosses over a couple of things.
First and foremost, it glosses over the sheer volume of D&D knock-off products that came out in the '70s and '80s. I'm not talking about the "near-D&D's" out there like Tunnels & Trolls and the 1st edition of Palladium FRPG. Rather, I'm talking about the plethora of outright D&D supplements that were published by third parties. The Afterglow web site was the best web resource for these products, but it has long since been lost to the Internet aether.
Afterglow2 is nowhere near as comprehensive or informative and hasn't been updated for almost 5 years, but at least gives you an idea of the volume I am talking about. That there was only one lawsuit that we have all heard of out of this (Mayfair) says something about the actual risk involved in publishing "generic" D&D supplements.
Second, the article misses one of the big points that came out of both the Mayfair and GDW litigation... That TSR, when faced with being unable to litigate the other party out of business, PAID THEM MONEY TO STOP COMPETING WITH THEM.
So, what it comes down to is risk. As to that, I can only repeat what I've told many a client, "Anyone can sue anyone for anything; the only question is whether they'll be successful." A basic question for anyone when considering a business venture is, "What happens if I get sued?" and in that respect game publishing is not unlike any other endeavor out there. To that end, all you can do is to be informed of what your rights are and insulate yourself from risk as best you can. (Insurance, incorporation or limited liability, and most importantly - TALK TO AN ATTORNEY - don't take advice from anonymous Internet message board posters.) Frankly, I think there are far more legally risky industries out there than game publishing. For example, if you are a landlord, it's not a question of if you'll ever be sued by a tenant, but when.
I think small rpg publishers and more importantly potential small rpg publishers are still living under the "chilling effect" caused by TSR's near-constant saber-rattling of 12 or 15 years ago, in which TSR earned the well-deserved sobriquet, "They Sue Regularly." However, I think history shows that when the publisher stood up to TSR, TSR lost, and that TSR's blustery nature did a lot more harm to themselves than good.
I think OGL is an interesting "deal with the Devil" in that you get express permission to use the SRD terms so long as you don't claim that your product is compatible with any trademarked game (i.e., D&D). From a cynical point of view, it almost seems like an open threat to sue people who claim compatibility with D&D. More generously though, I think the OGL went a long way towards getting more small game companies out there putting out art, and without it I don't think you see the OSR products I've been spending too much money on for the last 5 years or so.
As for the GSL, I feel much the same way about it that I did for the d20 license. It all depends on how important it is to you that you have that "is compatible with..." language on your product, Coming at the question from the point of view of a consumer who long ago lost any interest in what TSR or WotC considered "official" or "approved for use with..." that little blurb and symbol on the product has no weight for me whatsoever. But then, it's quite likely that I'm not among the audience anyone considering using the GSL is trying to sell the product to.
To sum up, while I am a lawyer, I am not your lawyer and am not giving anyone legal advice. If anyone is interested in exploring the legal issues of their particular situation, please consult an attorney in your particular jurisdiction as laws differ from state to state and from country to country.