I asked Sneeks about this Scutch, as I recently cocked up my apps by syncing them with iTunes, meaning they no longer work (simple delete and reinstall sorted them).
I now can't access Cydia and asked Richard, because when I went to restore, itunes downloaded 3.1 and asked if I wanted to upgrade. Apparantly, if you don't connect to the internet when restoring, it won't check the updates and you can restore to 3.0.1/3.0. Or he said Shift and click restore (or ctrl) and this allows you to choose which software you want to restore to.