However if your friend ever has a problem and needs to restore his phone they will need to restore to 3.1.2 or 3.1 because Apple has stopped signing the 3.0 and 3.0.1 firmwares.
Because of that... I would recommend that you consider using pwnagetool 3.1.4 to create a custom 3.1.2 ipsw and upgrade both you and your friend's iPhone to that version. Then you can give them a CD with that custom ipsw on it and explain how they can restore to that version if they ever have troubles again. Much safer than an OS that probably can't be restored.
If you really want to stay on 3.0 I would highly recommend checking out the firmware umbrella and seeing what Cydia has saved regarding your iPhone.