Yes - I did it and I would say it's becoming more common. The reasons for doing it are all the same as doing it straight out of an MBA program. The challenge is fundraising while you have a full-time job. Investors want to see that you are committed to the path. I actually quit my job before I had funding - I felt that I needed to invest all of my time into getting started. I wouldn't necessarily recommend that, but I had a decent backup plan and my wife was still working. My operational experience was quite helpful. I had 2 years as a manager post-MBA, so it was easy to talk about how I would manage people and operations since I had been doing it. Still searching, but I imagine those skills will translate well into whatever company I buy.

Plenty. I did it and I don't regret it. In the corporate world, you're promoted because you can act a part that the people around you like. It doesn't matter if you found and built a market that made the company several millions if the people above you don't like people like you. While this is true in entrepreneurship, I'd argue that it's more merit based than anything I could have gotten working elsewhere.