I have a Gen 4 Glock 19. I first shot it with PMC 9mm or some of the cheapest/underpowered ammo I could find. I had 3 malfunctions in the first 50 rounds or so. I swiched to 124 Grain AE and 500 rounds later not a single malfunction besides the first 3.
I LOVE Gen 4. I love the grip texture, the bigger mag release, and the significantly less felt recoil. I would say its about 20% less recoil than the Gen 3 Glocks.
Are people having problems with them? Yes. It appears the Gen 4 Glocks are more prone to malfunction in the first few hundred rounds ONLY when shooting with underpowered ammo. I shot some WWB/PMC just to make sure I was not having any problems with that ammo after my recoil spring had broken in. It worked fine, although I did have brass in my face a few times.
Morale of the story? Dont use underpowered ammo at first, if at all.
I live near Milwaukee. If you ever want to meet at a range sometime shoot me a PM.