I recently did a Startup Weekend and coded basically non-stop for a couple days. Afterwards I felt great, like my skills were being used to their fullest; and I had created something significant. It wasn't until days later that burn-out set it; but I wasn't burned-out from working all weekend, I was burned-out from my day job. How little real, valuable work I did at my day job compared to what I did during the weekend made me feel worthless and insignificant.

Paul Graham has talked about how heavy a work-load starting a startup is, and how much founders enjoy it compared to life at a big company in spite of it. I was skeptical at first, and thought that you had to be some super-human workaholic to handle it, but it turns out creating value is really enjoyable and fulfilling. It's a different kind of work, a kind that invigorates you rather than drains you.