[dmbaggett]

It depends on what kind of "hard" you're looking for. I've worked on games (Crash Bandicoot), search (ITA Software), and email (http://inky.com) and all have been hard, though in different ways.

Games are hard in that you're always trying to squeeze more into severely constrained resources, so you end up having to produce convincing but fake approximations of algorithms that would be far too expensive to run in their "real" forms.

Travel search was algorithmically very hard (see the few papers by de Marcken about this for a glimpse into this world).

Email is hard because it combines many disparate skills (design, UX, back-end scaling, protocol details) and because the MVP is incredibly complex.

All involved tremendous amounts of slogging.