My experiences with NiCds have been less than positive. I'm prepared to accept that the chargers I used weren't as good as the chargers I have now, but the NiCd cells I used put out a significantly lower voltage than equivalent alkalines and would poop out suddenly even after being properly cared for and recently charged. The memory effect also contributes to my negative opinion of them. I never got a decent number of charge cycles out of them.

For me, I'd rather use other battery chemistries and devices that won't overcharge them. I've had much better experiences with them.

My first 9.6v Makita NiCad battery packs lasted about 15 years. Sanyo NiMH AA's last around 10 years when they get to the 80% capacity mark and I give them to the kids. Energizer and Rayovac last 5-6, Radio Shack are more $ than the rest and last 3-4.
Anything Lithium Ion 2-3 years at most. I make sure if I'm buying a GPS, Radio, Camera, etc to buy the AA powered rather than the lithium ion.

Wow, that is almost exactly the opposite of my experience. I have LIon battery packs for my power tools that are ten years old and still good. I never had a NiCd pack last more than three. Weird.

That's not my experience. I have an old Palm Treo cell phone with a Li-ion battery. It's over 6 years old and still holds a charge like new. Li-ion has offered me the best experience with rechargeable batteries and has changed the way I view the abilities of rechargeable batteries in general.

You may have treated your Li-ion batteries in the wrong way. I can't recall ever letting that Palm Treo go below 40%, and I charge it every night. Some people tell me, even after hearing about my experience, to let that battery be completely discharged. I have to say with all due respect that I certainly will continue treating Li-ion in the same way I've been treating it.

You were doing the correct thing. Lithium ion cells work best when recharged often and not drained too far. But for long term storage, it is preferable to put them away at a 40% charge rather than a full charge.

Actually, that's why I keep non-rechargeable lithium batteries for flashlights that I think will sit for long periods unused. I want maximum capacity for those lights. But I will use lithium ions in certain EDC lights that I know I will use periodically and just top those off periodically.

Then again, the term "lithium ion" includes a range of similar but distinct battery chemistries so part of the difference in experience may be due to that, too. In particuarly, power tools usually use different lithium ion chemistries from consumer products like cell phones and digital cameras.