Those are easily the questions I feel the best about after answering, and really they generate the best encouragement by far. Much better than points is seeing this: http://i.imgur.com/POZmt.png
But compare the score of that tricky question to this very recent one, where both the question and answer garnered a lot of upvotes because the title was "why are my balls disappearing": http://stackoverflow.com/q/11066050/154112
Even with a bounty on the tricky question, hounding flippant questions can garner you more "reputation" far faster than giving thoughtful replies to hard questions, which can be a little disheartening.
"Also, very difficult questions get relatively few points compared to very easy ones when they are answered."
Yeah, this. It hurts my eyes to see that most of my rep on SO I got from A) Recommending the K&R for a starters' C book, and B) for explaining how the @ works for error message suppression in PHP.
While the numerous questions I answered that took actual experience and hard work, hardly ever get an upvote, let alone an 'accept', presumably because whoever asked it doesn't care enough about the issue to do the work required to solve a hard problem, even if the principles are handed to him.
This is one of the main reasons I hardly use SO anymore, myself.
I pride myself in answering some of the trickier questions in my domain, ie http://stackoverflow.com/q/10060242/154112
Those are easily the questions I feel the best about after answering, and really they generate the best encouragement by far. Much better than points is seeing this: http://i.imgur.com/POZmt.png
But compare the score of that tricky question to this very recent one, where both the question and answer garnered a lot of upvotes because the title was "why are my balls disappearing": http://stackoverflow.com/q/11066050/154112
Even with a bounty on the tricky question, hounding flippant questions can garner you more "reputation" far faster than giving thoughtful replies to hard questions, which can be a little disheartening.