There are currently 3 screens that Apple has on its different laptops:
1. "Glossy with glass" - this is what is on the standard MB and MBP. It is a
glossy screen
with glass on top. The glass is even shinier than the glossy screen underneath. Call it "uberglossy", if you will.
2. "Antiglare" - optional on the 15/17 inch MBP. This is actually a MATTE screen. "Antiglare" is a misnomer. Traditionally screens of this type are referred to as "matte", like glossy vs matte paint. Nowadays more and more people are calling this "antiglare".
3. "Glossy without glass". This is on the MBA. It is the same screen type as the standard MBP but does not have the glass on it. It is still glossy. Just not as much as the glass itself. It is not a matte/antiglare screen. It's not even "semi-glossy". It's a glossy screen, like you see on most other laptops nowadays, but probably higher quality than most.
Apple has created a new category of "uberglossy" because of the glass. That's because the glass is so damned shiny. But it's glass on top of glossy, not glass on top of matte. If you remove the glass on the MBP, you will not have an antiglare or matte screen underneath. You'll have the glossy screen a la MBA. In order for Apple to "customize" the antiglare screen, they remove the glass and then put a matte finish on the original glossy screen. Or they simply use a matte LCD that's been pre-made for the custom orders.
The glass helps concentrate the colors, acting almost like a lens. It also protects the screen nicely and is easier to keep clean. But... it's even more reflective than the glossy screen it covers.
The old Santa Rosa and Merom MBP models circa 2006/7 had this glossy screen without the glass, just like the current MBA. It's a nice compromise between matte and glass, but it's still glossy and still pretty reflective.
Too bad you can't get that on the current MBP. It's either glass or full-blown matte, which, due to the matte coating, does diffuse the light a bit and comes off as just a little bit duller. A bit. And it smudges easily and is harder to keep clean, like all other matte monitors out there.
It also reflects light, btw. A matte screen does not completely diffuse the light in all directions. If it did, it would obviously be unusable. Some of the light hitting the screen from external sources is still reflected back, but it's quite a bit less, which makes the difference for many users.
If you remain undecided, it's best to check them side by side.
I personally like the MBA style screen best. I don't mind a little gloss in exchange for the vibrancy and crispness it offers. But to each his/her own.