There are three things that Cataclysm may or may not bring, that makes me spin:
Primo - game mechanics: lots of changes, from hunter mana to focus change, dk rune mechanics, shortening talent trees, reforginig, extensive usage of phasing/shifting. The remake the experience and feel of the two most common classes will solve most of the bland issues (hunter mana) and bring some complexity to the playstyle (dk rotations), new talent trees with 24-32 mandatory talents will leave some room for utility/fun stuff that people tend to not pick up because of too many mandatory talents in TBC/WotLK, reforging will bring more variety to gear choices. Phasing is my favourite, because I love questing and advancing in storyline without a visible changes in the world was a no-go for me. It was well introduced in WotLK and Im happy that Blizzard want to use it more often.
Secundo - social aspect of the game: making 10 and 25 man share the same loot tables and ability to split/merge raids might bring back a depth in the social aspect of the game. I can imagine guilds joining their raids to beat content with the best geared / minded players or spliting them to smaller ones when there's not enough people on-line to form a proper raid. I think it will make a lot of room for guild2guild experience exchange and bring people together, making the community stronger.
Tertio - out-of-game facilities, espc those served by 3rd party developers: ive seen wowhead growing up from a small site, mmochamp becoming no1 source of inside-a-patch infos. Lots of great work was made by people interested in the industry and Im sure a lot will come. I, as a front-end developer and art director wait for those web-based facilities more than anything.
Nevertheless time will tell what Cataclysm will bring, things change fast and, due to not getting into beta yet, Im not able to contribute to the development as I was in TBC/WotLK betas. Maybe ZAM's network will give me this opportunity.