I've said this in other GC related threads before, but I've had mixed, but fairly good experiences at my local GCs. I just never assume that the guys working there know more than me (I research stuff I'm interested in before going in), and I've done alright. Most of the employees don't know much (And how could they? GC sells thousands of items), but they're generally friendly and helpful enough. I've had worse experiences at some of the local mom and pop places... Lots of attitude, especially if you don't play the blues or classic rock... And I'm not slamming those styles of music, just the snotty attitudes of some salespeople I've encountered.
I know lots of people hate GC and I respect that... I've had mostly good experiences there. I AM trying to cultivate a friendly customer/employee relationship with a couple of employees at a neighborhood guitar shop I occasionally browse. They seem genuinely nice... Although the now absent owner is definitely a prick. I can only justify buying there because I know the two I'm getting to know make a living working at the place. Plus it's less than a mile away, and carries tons of sweet gear.
Also, I have to say that although most of GC's employees seem to be youngish kids that don't know a lot, I've witnessed some of the crappy behavior that they have to deal with from customers first hand... And I've worked in retail... It's not generally fun, or as easy as it looks. I'll extend some good cheer, and try to be patient with GC employees unless they're being complete pricks... Which has never happened to me.