Same as OP. Been running an unrooted DI for almost two years and things were starting to lag. Did a factory reset and once again amazed at how fast this phone is. Thought long and hard about which apps I really wanted to reinstall and probably only did about 2/3. Phone is running great.
All that said, I think I'm going to try the iPhone 5 when its released this year. Been on an Android device for over two years now and simply ready to try something new. Will hand my DI down to my wife who is still on a rooted Eris. She'll love the DI.