The jailbreak tweak Intelliscreen X is one of the most powerful and amazing things I've seen related to iOS. If Apple were to pick up another jailbreak dev, this guy would be an awesome addition IMO. Not sure how likely that is, but I can dream. I'll be really happy if half of its functionality is added to iOS in the future. It's usurped SBSettings/Springtomize as the reason to jailbreak IMO.
Definitely take a look if you've never heard of it.
http://www.youtube.com/watch?v=zwx9PUX_tz8 note: this video is of the vanilla version, there have been many great plugins/add-ons released in the months since release