I too have a pre-production UBR that I used for a few years over here.
It never failed me and is still in good shape. The only issue I had was with dust and dirt. First of all, pouring dirt or sand into anything is not a very good test. Mine sucked up the fine Iraqi dust and it did change the way it operated over time. The latch became slower and a few times it didn't even want to open, but it did with a bit of force. It took about three months of constant abuse to get this way. So, with a little bit of preventive maintenance, it should not be a problem.
Here are some pics of the level of crud when it became hard to operate.
http://i34.photobucket.com/albums/d1...nja/dirt-1.jpg
What I like the most about it is how it shifts the weapon's center of gravity towards the rear. This may be important to some. For me, I want to be able to shoot one handed, since that is all you might have left (pun intended).
I stopped using it a few months ago because I simply didn't need it for my work. My M4 is not burdened down with additional items. I went back to using my ACS to make it easier to use inside of vehicles.
All my Magpul stocks are rock solid and well built. Because it never failed nor broke, it gets a big thumbs up from me.

