I actually can't stand matte screens anymore. Been using a glossy screen for some time now on various computers and (IMO) you get a much better experience for watching video and playing games.
I don't do graphics work, and quite frankly I don't think anyone should be on an iMac -- they should be doing it on a Mac Pro.
Not to get off topic, but there are loads of semi-professionals and consumer hobbyists doing graphics/video work on the iMac, and they can produce some great stuff. Sure a Mac Pro is better, but no need to make that leap if it ain't necessary!