I would like to interject my two cents here real quick.
It would be really nice if there were demos released closer to release dates. I'm not saying before the game comes out, but let's take Halo for example. I personally love Halo, on Xbox and PC, but how long did it take after the PC version was released for the demo to show up on the net. I do know a number of game magazines do also have demo discs with their issues, which is nice as long as the demos are in a timely manner.
I am lucky to be a broadband user, and can download whatever, so that's not an issue. But it would be nice if within a week a demo was out for a game that was just released. Maybe I'm mistaken, but I wouldn't think it'd take much for a developer to release the first level of a game as a demo just after the retail product hits shelves.
However, I too have a number of bad games in my collection, and I take sole responsibility for not researching my purchases before plopping 50 bucks on a counter for a bad game. Maybe it's just me, but I've always found plenty of web sites and magazines to give me information about a game (or whatever else) before making the purchase, and sometimes I get caught up in the hype and lose some money, but oh well.
But to say something on topic, I must say that these leaks are just...well...dumb. It's an interesting idea to say, "I beat x game two months before it was released," but you're playing through an unfinished work. If you have the patience to work with the crazy bugs and unpolished code, the more power to you. Again, maybe it's just me, but waiting a couple more months for a game to come out so they can finish whatever they feel needs to be finished is fine, gives me more time to finish the million and one games I have that I've never completed yet.
EDIT: Okay, so maybe it wasn't real quick