[jtfairbank]

I can't say as a PhD, but I started my current company as a senior in college. I spent two years working on it as a side project (including building the alpha and talking to users), then jumped the bridge as soon as I was able.

In short, my grades suffered. But school as a whole is less important to me- I am doing what I wanted to after school, just a bit sooner.

If you want to start a company during your PhD, be prepared to give in one way or the other. Wrap up your PhD with as little work as possible and as quickly as possible. Bonus points for aligning your PhD work with your startup work, but be careful about allowing the school to make claims on the startup. If you choose the PhD over the startup, maybe don't go full startup yet but begin quietly building the product and talking to people in your free time. Then launch and grow as soon as your PhD is done.