Now I have my own office with a huge window, my guitar and skateboard hanging on the wall (they both get a lot of use throughout the day), and I make more money on average (to my own surprise) than I did as a full-time engineer.
I wouldn't trade it for the world, and if I hadn't tried, I'd probably still be sitting at my same miserable little desk in that same miserable little cubicle, with the same slightly wacky boss.
DISCLAIMER: I had started down the entrepreneurial path a few years before I quit and had spent every waking moment on my own companies on the side. I wasn't making enough to quit when I did quit, but I had lined up a few months' worth of contracting work, and figured that would be long enough for me to get on my feet.