It looks like a cap rated at 4000h @ 105deg C should last around 60 years at 100deg F or so. Anecdotally I have a guitar amp made in the 60s with the original electrolytics still working. Sounds great.
As per my other comment on this thread, you can intentionally decrease the lifetime (aka MTBF) by running the part at 10 or 20% overvoltage, in addition to extreme temp, to create a corner case and stimulate premature failure in reasonable amount of time. 20% overvoltage won't kill the cap, as any part has absolute maximum ratings well beyond what the spec sheet says. Even bad caps have some degree of guard band, else they would never leave the factory.
Interestingly enough I have heard in a few places that there is a 'sweet spot' in terms of duty-cycle that extends the life of electrolytic caps... I would that that high-use electronics (or 'always-on' devices) probably miss that spot.
http://www.rubycon.co.jp/en/catalog/e_pdfs/aluminum/e_BXF.pd...
Lifetime is specified at 10000hrs at 105deg C.
As temperature decreases, lifetime appx doubles per 10deg C:
http://www.low-esr.com/endurance.asp
It looks like a cap rated at 4000h @ 105deg C should last around 60 years at 100deg F or so. Anecdotally I have a guitar amp made in the 60s with the original electrolytics still working. Sounds great.