If you're a WoW-player, you'll be interested in this interview over at 1UP that covers the upcoming Wrath of the Lich King expansion. Although there's not a lot that's new for the expansion as a whole, there are a few Death Knight tidbits tossed out by the devs near the end of the chit-chat. (If you're still stuck in the Dark Ages and you have no idea what a Death Knight does or even what it is, then here's the official Q&A for you.  There's certainly a ton of lore to look through in the official links!)

In the 1UP interview, the devs speak of how to unlock the Death Knight. In the next expansion, Wrath of the Lich King DKs will become accessible through doing a series of quests (this of course is apt to change). The devs also speak about the way DK spells are cast (using, instead of mana, runes) and giving additional, new details about rune cooldowns and the emphasis placed on the frost, blood, or unholy magic schools. Consider:

In general, Blood abilities are damage oriented, Frost is control-oriented, and Unholy contains utility and damage-over-time mechanics, but that's not a hard and fast rule. "We don't want to pigeonhole it to the point where when you're tanking you use all Frost runes, or when you're DPSing you use all blood runes.... There are inherently good reasons to use a mix, and even if you have at least one rune type on the bar, you'll have access to all your abilities should it become necessary."