Disc dps is nothing to laugh at. We're not the best healers because we can dps, we're the best dps because we can heal

You stack haste + spellpower, go smite spec + smite glyph + power infusion + shadow fiend and you can pump out some really nasty damage.
I haven't played the comp much further than 2K, but I've seen some videos. It's not really a faceroll comp if your opponents play well, you basically have to catch them in a bad spot and you and your partner have to give it everything you've got all at once. Or you might have to turn it into a control + mana burn game, but that can also be very difficult if your opponents don't have down syndrome. Be prepared for some very long games. If you and/or your priest don't know how to fakecast, you're going to fail. Get an add-on that shows enemy interrupt cooldowns and I'd recommend spell alerter for your priest so he can be super quick with his dispels. Because of spell alerter I can start spamming dispel before the spell even lands and you'll be out of CC instantly.
http://www.warcraftmovies.com/movieview.php?id=124673
http://www.fileplay.net/file/7561/hydra-7
Both of those movies have some nice clips of disc/frost.
The main thing I have to say after carrying so many mages and warlocks to 1800 is
USE YOUR CC. So many fucking baddie terribles that fear or poly once every game. You can keep people out of the game for 50% of the time with poly, 50% of the time with novas, 30% of the time with counterspell, 30% of the time with psychic scream, and then you've got some stuns to throw around and some situational mind controls. You're a mage, your deal is CONTROL, so use it! And use it with your partner to create infinite CC chains!
One last thing I'd like to say is shadow/frost is just as viable as disc/frost and the games will be over much quicker. SK100 shows plenty of teams running both comps at 2700+ ratings, so don't re-roll comps if you're just looking for easier victories.