I am definitely seeing the 'end' of the cap where I simply can't put more time into it. So far I have held up really well though, and I implement most of if not all the changes that people want to see (if I feel they are a good fit, that is).
But yes, my traffic is growing every day with more and more users, and adding new features is starting to get somewhat daunting as my code base grows.
As far as marketing, accounting, programming, etc I do it all, with the occasional help from a friend when it is too much.
Highly recommended though :) My site is my baby, and the goal when I made it wasnt to make lots of cash... it was to make a LARGE site that everyone uses. ever since I was a kid I wanted to create a massive site with thousands of users, and so far my dream has become a reality. it is a very good feeling.