candlepowerforums will answer all your questions and more.. As people mentioned already, the benefits I see in Lithium is:

Shelf Life
Weight
Longevity
Cold weather

Exactly in that order.. You can get Lithium Batteries in AA and AAA(energizer, not cheap).. Have them and use them in my EDC, BOB, and stocked at home and car. The Used by date? 2020

I actually use 2 AAA Lithiums in my EDC LED flashlight. Please note that the initial output of Lithiums tend to be higher than 1.5v. Double check with your electronic manufacturer to see if they accept Lithiums.. Another way is just to run the batteries in a high drain device temporarily, and then transfer the batteries over.. (me, I just put them in) <img src="/images/graemlins/smile.gif" alt="" />

In regards to weight, I just weighed them on a kitchen scale.. An Energizer AAA Lithium weights in at 7 grams whereas a Duracell Ultra (Alkaline) AAA weighs in at 11 grams. So 3 Lithiums will weigh less that 2 Alkalines..