I have owned and still own a number of Glocks in different models/calibers that are various ages, the newest being purchased late in 2007. I have carried them for work guns and trained with them quite a bit. I carry one now as a personal protection piece. I have heard of some agencies having trouble, but I have never personally observed any Glock breaking. Sure, it can/could happen. As has been stated, anything mechanical and manmade can break.
Glocks have never broken for me. Indeed, I cannot remember any malfunctions that were not due to ammo (a dead primer is a dead primer no matter the gun). I cannot say that of most of the numerous other brands I have owned and used. Therefore, I carry Glocks and will be very comfortable doing so until something better comes along.
Now, as for someone in a store having a loud opinion etc. There is a creature (closely analogous to the Mall Ninja) that seems to be at work in the original post. That is the dreaded "gunshop commando". They are not rare, unfortunately, but they are easy to spot. Broad, sweeping opinions backed up by nebulous history and vague sources mark their speech. Beware.......