What I find really interesting after mulling it over.. is that there's soo much crap out there -- being made well by really really talented people. I wonder if there's an easy heuristic to figure out if something is worth doing -- I think that we've exhausted the whole-> "do what you are passionate about" and "solve problems" bit as a source to figure out what to work on. Or have we?
I think passion is the best heuristic. Otherwise it depends on things we cant know. Will we be invaded by aliens in 1000 years? If so then thats going to change the optimal side project!