If stem cell research eventually results in a way to radically extend the length of human life, how would our soicety change? Let's assume that it's cheap enough for everyone to afford (although you may argue that some group of elites would try to restrict access). Perhaps a constant supply of the drug is needed to stay young forever, or perhaps it's a one-shot deal. Either way, people just plain stop dying from natural causes -- but bullets and car crashes can still be lethal, of course.
So how would society change? I'll toss out a few ideas without a lot of justification (some seem obvious to me, others are mere speculation).
1. Political jobs would all be term-limited.
2. Income tax would be eliminated in favor of a wealth tax.
3. People would either stop driving, or would drive tank-like vehicles (which would be financed on 100-year terms).
4. The price of real estate would increase, at least until the supply expanded through space exploration.
5. Medical doctors would be almost entirely replaced by biologists and gene therapists.
6. Denists would need to find a way to make our teeth last longer... unless the stem cells let us grow new teeth. Maybe we'd all get artificial teeth implanted into our jaws.
7. Depending on how the stem cells worked, fertile women might become scarce. Unless the stem cells would differentiate into egg cells women would still lose their fertility in just a few decades (by running out of eggs), while men would stay fertile their whole lives. This could lead to the rich and powerful men using their influence/power to attract all the women young enough to bear children. Some women already sell their eggs and even carry babies for other people, and that would probably become more widespread.
8. Interest rates would change. Would they move up or down? I think down, because people would be willing to settle for lower returns on their money since they'd have much more time to accumulate wealth.
9. Following #8, all financial business would become more risk adverse.
10. Space exploration would be done almost entirely by robots, until space travel was nearly 100% safe.
11. Of course, people would need to leave their houses less in general, since most people would working from home (or wherever they want to be).
12. Suicide would become the number 1 cause of death.
13. We'll discover a whole host of new medical problems that can't be solved by stem cells.
14. Likewise, we'll discover a bunch of new mental diseases.
15. The vast majority of people would never be able to retire.
16. What about marriage and divorce? Would everyone eventually end up divorced at some point? Would anyone get married anymore? This may depend on #7.
17. Prison sentences would get longer.
18. Depending on #7 again, the population might increase much more quickly than current rates. People might be expected to sterilize themselves, and there may even be laws put into effect for population control purposes, depending on #4.
19. What if stem cells in the brain cause humans to revert back to their pre-adolescent mental abilities -- without concrete reasoning?
20. People would change their hobbies around, resulting in scads of awful poetry and artwork.