Yeah my unlocked iPhone was misbehaving too, just did a restore thru itunes and it mostly sorted it out. You will lose all your apps, but you can restore from the iphone backup in itunes which remembers which playlists were syncing, has a backup of all your contacts/sms/mail accounts/wifi setings/call history etc.
Straight after you restore your phone thru itunes, you must say to restore from this backup when it asks you, or else it will be gone for good though.
Once that has finished syncing, visit jailbreakme.com to get installer again, and reinstall your apps.
Personally I have found a relationship between how many apps you have on your phone, and the overall speed/stability of the thing. I think its important to keep it as empty as possible and just install the apps you really want. You have to remember that the hardware is quite limited (esp RAM), and the phone has not yet been designed to run third party apps, everything we are doing are just hacks that most people assume will work 100% fine.
For me the essentials are: installer.app, BSD Subsystem, OpenSSH, and Services, which is useful for turning SSH on and off to save battery life.
Next would be summerboard for themes/scrolling home screen etc, and then a few cool games like Labyrinth, Mines, and Lights Off.
Just remember, the more apps you install, the more instable it may become.