Remember when you were growing up and your parents bought you a Huffy bike at Kmart? Then some neighborhood kid got a brand new Mongoose with mag rims, pegs, blah blah blah blah blah. His cost more than yours, looked cooler than yours, and dammit, you were jealous (I was). The thing was, he didn't have half the stones it took to go off any of the big jumps that you did, and when he did take off the training wheels and try anything big... FAIL. QQ. You may have been riding a Huffy, but dammit, you rode that bike and did it well.
Hopefully, my point didn't get lost in that analogy. In case it did, bike = gear.
But seriously, when did an arbitrary number start to reflect the value of a person in a raid? Ok, I'll give you that the number isn't totally arbitrary, because it is based upon the level of the items worn, but here's the problem. I have seen, on more than a few occasions, a main healing spec player wearing dps gear (or even pvp gear with agi/str) just because it had a higher GS. During the raid! I've seen resto droods with resto tier gear gemmed for HIT! Really?!?!?!
Now, obviously, the majority of players don't fall into this fail category. I'd like to think (and please let me be right) that most people at least understand what each stat means to their particular class, but lets be honest. Since GS (and to a slightly lesser extent wow-heroes), have come about, people are under the crazy impression that item level = upgrade. Even more people are under the impression that higher GS = better player, because "hey, they must have experience to have all of that high level gear." /facepalm
I can't say that GS doesn't have a place, but it's become not only a crutch for group/raid/guild leaders, it's become the sole yardstick in some cases. How many times a day do you see on trade chat "
forming. come to sb steps for gear check. 5k GS min"? I have a little over 5300 GS currently, and I'm rarely anything but tops on heal meter (yeah, I'm a resto drood and that's kinda easy to do when you're rolling hots on 10 or more people, sue me), but when I was at 4300 GS, I could heal as good or better than other druids with over 5k GS. Why? Because I was gemmed/glyphed properly, know my strengths and play to them, and I know just stacking one stat makes a well-rounded healer. Here's some examples of why GS isn't the end-all be-all that it's getting billed as (I'll speak to resto druids because this is what I can relate to you most easily, but I'm sure anyone else can remember seeing similar things with their own class.)
Case 1: I'm in a raid with another resto drood. He's got 5.5k GS, well over my 4.8k GS at the time. He's stacking spirit and mp5 gems... lots of them. A few +int in there too. I have about 22k mana; he's got about 29k mana. We have a nice long boss fight. I don't run out of mana, but at the end of the fight, I have about 4k mana left... he has 21k. I DOUBLED my healing over this guy and our overhealing was about the same. So in this scenario, you have someone with a much lower GS out healing someone with a higher GS because the person with higher GS was improperly gemmed (not that mana regen is bad, but hello excessive), and I also rolled hots properly.
Case 2: This is, I'm sure, quite common. I ask a new guildy druid what spec he is. Boomkin with resto offspec "but I'm over 5.1k GS in both". But he's not over 5.1k GS in both, and here's why. Boomkins (should) be gearing for +hit and +crit. Resto +sp and +haste. A lot of boomies out there take resto as their offspec because "it's easier to gear resto because a lot of the gear is interchangeable". I sigh at this. You can't swap out 5 or 6 pieces of gear and expect to heal as well as someone who is full-time resto. This isn't just because the FT resto player knows the spec better (we would hope), but because every piece of gear is tied together to round out the spec and healing style of the player. Sure, he should be able to handle healing heroics no problem, but don't think that he'll be able to be the "z0mg 1337 haelz!!1!1!" in ICC. Sure, he can step in and fill that last healing spot in a 25man if the other healers are all better in their roles. GS does not a healer make.
Case 3: I'll make this short. A resto drood wearing 2 pieces of melee pvp gear. I pointed this out to him. His response is that it was better than what he was wearing before. I said it's not for healing, it's for melee. He said "yeah, but the gs is higher". He wasn't kidding. /facepalm
My point in this is that GS is just a tool. It is not the Holy Bible of proper gear. I'm not saying that you should invite someone with 2800 GS to your next ToC, but think before you blindly exclude someone with 4800 GS and invite someone with 5200 GS. They may have a Mongoose but have no idea how to ride it.