Yeah, that's roughly my plan after I get my DK up to 85 and really learn the new move set. Right now I'm still kind of up in the air over whether frost or unholy presence is going to be a better bet for optimal output. Frost seems to be more consistent, but unholy seems to be better in some encounters. It's a welcome change from when blood was the only usable combat presence and unholy was only used when you wanted to spend half of the battle auto-attacking while your runes came off cooldown. It's nice that haste is actually good and that some abilities reduce rune cooldowns. I'm extremely happy with how Blizzard treated that class.
I'll probably move over my priest and see how he fares as well. Blizzard apparently made some pretty substantial changes to healing and mana regen, so I think it'll be interesting to see how it goes. Both healing specs start with the mana regen talent that used to be in the discipline tree, so I can't see it being too much different aside from spirit possibly being downplayed in the holy spec, but we'll see. Hopefully Grid and Clique either work or have been updated to work with Cataclysm, because healing the old fashioned way is like totally lame and stuff.
Other than that, I really want to see how low-level questing is now. Looks like the world is a bit less sparse in terms of mob count, so it looks like you're a lot less likely to get jumped at low levels. Guess I'll find out soon enough.
I also love the automatic quests. It's great for steering you in the right direction when you go into an unfamiliar area. Aside from that, I like how killing some mobs can activate quests (like the eel killing quest in Vashj'ir). It's a nice way to get some extra coin and experience, and the fact that some of them don't require you to turn them into an NPC is very convenient.