As for durability, many people who own a Toyota Rav4 EV still have their original NiMH battery pack after over a decade, driving over 150,000 miles. NiMHs are pretty tolerant of abuse compared to NiCads while not losing capacity over time (regardless of usage) like Lithium-Ion. The only real problem with NiMHs is that any NiMH large enough for a car is prohibited by Chevron, who owns the patents on them.
Nicads longevity depends largely on how religious you are about cycling them (they have a terrible memory effect) since if you only partially discharge them before throwing them on the charger (like many people do) then they go downhill quickly. It should tell you something that two of the NiCad packs in my R/C car which get run down to near-death then hooked to a discharger before recharging, lasted over 15 years while the NiCad pack in the cordless phone was crapping out about annually.
Lithium-ion packs degrade with temperature and exposure to air, but it’s safe to assume that under normal usage at normal (room) temperature, they will lose 15–20% of their capacity per year whether you use them or leave them on the shelf. That gives them an effective life of 2–3 years.
@uberbatman My S 860 seems to get more shots out of a set of NiMHs than a pair of alkalines. I tend to carry a spare pair of AAs when I take my camera out, but the last time I tried alkalines in my camera, I went through both sets in less than 50 pics as opposed to 70–100 pics per set with the 2500mah NiMHs.