When I upgraded my iPhone to 2.2.1, I did a full restore on my phone. I backed up everything and wiped the phone clean. Man, it was fast! Check out this link to keep your iPhone in top shape:
How to have a blazing fast jailbroken phone
Anyways.. after I did this, my phone was indeed fast. However, all my notes that I had in the Notes app was un-editable. In fact, I couldn't create any new notes, or delete the current notes. 2 weeks later, I finally get time to fix the issue. Here's how you fix it: (Thanks to the MMI forums)
SSH into your iphone go to /private/var/mobile/Library and change the owner to the Notes directory and it's files:
Open up terminal in WinSCP, and type:
chown -R mobile Notes
and test if you can save or modify any note.