Can someone please tell me what the difference is between drop-free and non-drop-free and the advantages of one vs the other??

Thanks!

drop free were the original glock mags, they were designed to stay in the pistol until it's empty.  the newer mags were designed to drop free of the weapon whether or not they were empty or full.

should say

NON drop free were the original glock mags, they were designed to stay in the pistol until it's empty.  the newer mags were designed to drop free of the weapon whether or not they were empty or full.

The original Glock mags were NDF. Glock figured why would you want to drop a fully loaded mag. I find with 5-8 bullets left in the mag it does drop free.
DF mags are supposed to drop from the pistol. I find they don't always drop easily. Most folks who compete in some form of shooting sport like the drop free's better because the magazine changing time is quicker.
DF mags are full metal lined and NDF are not. You can easily tell the difference by looking at the mags. Go to Glockmiester they have pictures.
Oh by the way a little Armor-All on the outside of the mags every so often makes all of them drop better.

I only like drop free mags as they make for faster reloads. Drop free mags have a square indent in the metal that sticks up above the plastic on the back of the top of the mag. Nondrop free have a round indent. Drop frees are only going for about $10 more then non drop frees.

Wow. You think there may be some Glock nuts on this board ?

I'm not a Glock nut, I just pretend to be one on this board.

Actually, I happen to own a couple glocks and have both NDF and DF mags. I'm not a nut I just shoot the pistols well....What can I say?

what gave you that crazy idea?

handguns.ar15.com/forums/topic.html?id=991

The NFML (non-fully metal lined) "non drop free" mags also have a base plate that is more but not totally) flush with the bottom of the grip frame. The top half of the base plate is beveled and fits into the bottom of the well.  A minor concern, but some folks like that for carrying their G23 IWB under a T shirt (every little bit helps).  
The other plus is that if you have a holster that does not cover the mag release proprly and rigidly, and you put pressure on the gun when you sit down, it can pop the mag release, leaving your mag not secured.  It may fall out sooner or later.  A full NFML will not.  I personally know of two Agents who this happened to. One of them swore his mag had been stolen until he searched his truck and found it in the seat.  Some of these guys carry mexican (yeah, I know, but you can't tell them nothin'), some carry with a variety of personal holsters.  Issue paddle holsters and web gear cover the mag release rigidly.
This is a much greater issue if you have an extended mag release such as the one issued on the G35 (My favorite gun of all time, but mine wears a G22 mag release).      

I'm going to go out on a limb here and say for concealed carry I prefer the non drop free.  When I carry my glock 22 I don't carry a spare mag.  If I need more than 15 rounds of 40 S&W then I probably need my AR or need to "haul ice" and get out of there.  Therefore, I don't want a mag in my gun that's going to fall out accidently.  Plus under the stress of a urban combat situation you could accidently hit the mag release or it could get hit while you are ducking for cover.  

Just my $0.02.