I think about this and look at it way too much. I have 4 level 80's and a 72 (which was my main throughout vanilla and most of TBC). All of these toons have dual-spec so I often play them in multiple ways and have multiple sets for them. So I am always looking at tier-set bonuses versus upgrades that break these bonuses (including the next level of tier gear). The majority of this expansion (WotLK) I have liked the 4-piece bonuses for my toons but often I do not like the 2-piece bonuses. Blizz seems to struggle with creating new set bonuses for each tier.
This is what I'd like to see in Cataclysm:
The 4-piece bonus from each tier becomes the 2-piece bonus for the next tier up. So Tier 11's 4-piece would be Tier 12's 2-piece bonus.
This would help alleviate some of that hesitation to break the previous 4-piece bonuses as you move on with progression.
Any opinions? I know this isn't the proper avenue to suggest this (Blizz's forums would be better) but I enjoy mmo-champion quite a bit more than reading/posting on their forums.