Keep in mind that some LED lights (Surefire is one, I'm pretty sure) specifically say not to use lithium batteries.

Ken

just like 3 people before have mentioned. I use Eneloops too, because of there good performance and low self discharge. Besides it's cheaper and more enviormently friendly on the long term. I use a normal "inteligent" charger.

That doesn't make any sense. Most Surefires use 123 batteries which are Lithium. Thats one reason i don't have any surefires because they don't have any that use AA's.

I have found that quality varies greatly in "intelligent" chargers. Those Energizer/RayoVac/Duracall chargers you can buy in reatil stores are not very good for long term use of re-chargeables but since most people don't have lots of them and track their usage they will never know that they only got a couple hundred cycles out of a set of bateries.
I found that once I bought a MAHA charger my batteries started lasting longer and old ones that weren't working very well and I was ready to replace started being useable again. So this time around I bought a decent charger to protect my battery investment. The charger was only $40 and I spent $25 on a charger for WalMart before so it wasn't that much difference.

Correction - I wrote Surefire, but I meant to say Streamlight.

The Streamlight Propolymer 4AA product instructions say "Use only Alkaline batteries"

I've read someplace that it has to do with slight differenes in the voltage.

On the other hand my Princeton Tec EOS headlamp instructions says it can use both alkaline and lithium batteries.

I have switched to lithiums for my Fenix flashlight. I haven't done any controlled testing, but they seem to give me a lot longer burn time. The light is used fairly regularaly, though not really an EDC.

The rest of my lights are CR123s. Harder to find, but they have an incredible shelf life. I keep one set in the EDC bag, and so don't change them until the light dims.

Some AA lights say not to, even the old incan Mag lights say to use nothing buy alkaline. I only use the Lithiums for long term storage anyway, those are the backup for the backup.
Any short term situation or using my gear for camping or testing I use the re-chargeables. Then is the re-chargeables are all discharged and I can't charge for some reason I have alkalines and then for long term worst case I have the lithium. If it gets bad enough that I need to use the Lithiums then I'm probably going to be very careful in how I use them.
I typically rotate the alkalines in my gear once a year and the ones that came out of them go into clocks or kid toys so they don't get wasted.