jremington:
Lithium battery protection circuits are available that will automatically switch off the battery at a certain cutoff.
They normally have a cutoff of 2.4V, a bit on the low side for safety and long battery life reasons.
I look at those safety circuits as a latch ditch safety circuit for when a proper cutoff circuit fails. I would not want to use one as a routine method of over discharge protection.
If however they were available in 3V versions.