I don't have a gen 4 but know people that do and some have experienced issues.I've got 2 gen 3's and have never had any problems with either one.Get a gen 3 IF you can find one at a reasonble price and don't look back.
I've heard similar stories, but with my line of work, I'm wary of potential internet tales. I'd like to get a gen 4 so I can reduce the back strap to fit her hand. I'll be trading a two tone 1911 for one hopefully.
now for the long story....
Glock had a recall on the recoil spring assembly with the first production run models. If you find a deal on a used one just call glock and if yours is on the list they will mail you the newer revised recoil spring assembly.
here's the link to glock explaining this. http://us.glock.com/customer-service/re ... g-exchange
If you get a new one they've been fixed for a while so you shouldn't see any problems.
After handling the gen 4 I traded my gen3 17 and 26 immediately for the gen 4 models. Got the 17 used and it was on the recall list. Glock had the revised recoil spring assembly in my mail box within a week. Keep in mind I had no problems with the original.
Also there are visible design differences you can look for in the recoil spring assembly before you buy. heres a youtube video http://www.youtube.com/watch?v=b_ojw6LDibs
Now if I were to stumble over a deal on a used gen 3 I wouldn't hesitate to scoop it up, but the gen 4 changes to me worth another $75-$100 over the gen 3.
Thanks for the info, everyone. I'm pretty familiar with the differences in the 3 and 4 having owned a Gen4 31 and currently own Gen 3 22 and 34. I'll look for a Gen 4. I like that they come with 3 magazines as well.