I was under the impression that colour reproduction etc was a lot better on the glossy screens. The main reason you'd not want a glossy screen is if you were intending to use it with a very bright window behind you, or outside in the sunshine.I did. It's a consumer feature, only wanted for an end user watching movies, not exactly a pro feature for people using their computer to actually create contents.
Frankly if you're using it outside in the sunlight or with a bright window behind you, then you weren't serious about your image editing etc or whatever you were being a "pro" editing.
I'm very happy with my glossy screen for when I'm editing my photos in Aperture.