I've used my (previous) matte MacBook Pro and my wife's MacBook outside. The MacBook's glossy screen is way easier to read in direct sunlight.
Glossy screens are harder to calibrate, and while they look punchy, they can give people who need super-accurate colors for photo/pre-press work a tough time.
For general, non color-accurate work, including games, movies, word processing and such, the glossy screen gives things a very contrasty, saturated look that many people like. Its great for DVD movies.
I have machines with both kids of screens, and overall prefer the glossy. But then again I'm not a professional artist. My laptops are mainly for text work, Keynote, spreadsheets, email and web. The glossy coating I think gives everything a very smooth, punchy, printed look.