I just emptied my bank to make room for Cata items, but had to make a painful decision: choose which tiers gets the boot and which stay in the bank. Personally i kept my T8 white set because in my opinion it's both the best-looking paladin set of WotLK, and the set that helped me defeat the most WotLK encounters. My purple T10 will also occupy a few bank slots as soon as i'm done replacing it with Cata greens/blues, but will most likely get deleted if i run out of space at some point.
Careful, this is not a "vote your favorite WotLK tier". I'm asking which tier you will keep in your bank to remind you of old good Naxx/Ulduar/ToC(lol)/ICC while you're raping Deathwing's face.
Poll is up