Will resetting my unlocked phone to factory settings lock it again? I have an unlocked G1 that is freaking out on me in various ways. If I "restore factory settings" am I going to wind up locking it?
Normally unlocked phones are unlocked for good.  I wouldn't expect a factory reset to change it.  (See also: Unlocked Galaxy i7500, Reset Will Remove it?)

It's not 100% certain, though.  For example, some Galaxy S users had their phones re-locked when updating from 2.1 to 2.2, which is a somewhat similar process to doing a factory reset.

You could always do a backup through ClockworkMod or something (and back it up to your computer first) in case it does get re-locked, so that you could restore it to the previous unlocked state.  That requires root, however.  (Root can sometimes be undone by a factory reset, but not if you have a custom ROM that came pre-rooted).

If you have the unlock code from when you originally unlocked it, that code should still work to unlock it again if it gets re-locked.