The leveling guide will continue shortly.
In Cataclysm, hunters are going over to focus. I've heard that in the pre-release versions of WoW, focus was the planned resource system for hunters, but for one reason or another, we got switched to mana. This is probably the biggest change I saw for hunters coming out of the eventual 4.0 release; I'm looking forward to it. It'll take some relearning, but we simply have too many stats to watch right now. Cutting Int out of the equation entirely is good. I have a level 74 rogue, so I'm not unfamiliar with that style of resource.
Haste, on the other hand, will change some things. Haste will make focus regenerate faster, but since it won't affect our attack speed, that also means that our autoshot speed is probably going to be less mutable, and Rapid Fire and Improved Aspect of the Hawk procs will be more important to watch.
Attack Power on gear is going bye-bye. (/cheer) I loathed the switch from 2 AP from Agi to 1 AP from Agi and AP on gear since it happened. (From my enchanter's point of view, things are going to get... weird. All those Spellpower and Attack Power enchants are probably going away - possibly to be replaced with Agi, Int, and Str enchants? We'll find out!)
The change to talents - paring out passive stat/damage boosts for "fun" talents - should prove interesting. I play heavy MM in both my specs, and 5 more points means you should be able to invest enough into a 2nd tree for the first or second mastery bonus.
I like that we'll be coming back to Azeroth. I'm looking forward to underwater mounts. (I'm sitting at 90 pets/90 mounts right now.)