If you use the search functionality of these forums, or just browse through the Journalism & The Media forum in particular, you will find plenty of information from articles and government reports about long-term use of hybrid vehicles. Edmunds has long-term vehicle reports for numerous vehicles including several hybrids (Prius, Accord and Lexus RX400h).
Contrary to popular belief, hybrid technology is not new. You'll find lots of info about that on this site too, but there's also a long article on Wikipedia
(http://en.wikipedia.org/wiki/Hybrid_vehicle). Additionally, the Prius has been on the road in Japan since 1997 and in the US since 2001 (model years). The Honda Insight has been on the road in the US since calendar year 1999. I'd say that clearly demonstrates these vehicles are not just a fad or a phase.
Personally, I plan to drive my TCH for at least the next 10 years. Historically Toyota vehicles have excellent logevity and I don't think it will be any different for the hybrids. Personally, I have no reservations about the potential longevity of my TCH.