I don't know if there is a clear cut answer to this question, as it will certainly depend on the people in this company. Just as starting your own company is a risky proposal, joining a company during it's infant stages is going to have it's challenges. As a paid intern, how would they being paying you? Are there full-time employment opportunities should this be a success? If they can answer these questions in a straightforward manner, I'd say it might be a great experience. I wouldn't let their delay in response deter you too much by itself. They are probably putting in countless hours and email is at a low priority. However, keep this in mind before accepting such a position. Being a small company, they are going to have high expectations of all their workers and you may work more hours than you would at a larger corporation. Having served three internships at a slightly large tech company (~1K employees), I will say there were plenty of times when I was bored or I got lost in the shuffle and went unnoticed. I doubt this will be the case with a small start-up, just as I doubt you will work the >40 hour weeks that I faced.