I've witnessed first-hand three start-ups slowed or stopped by "ninja" developers using the start-up as an excuse to try some cool new technology that will look

I've witnessed first-hand three start-ups slowed or stopped by "ninja" developers using the start-up as an excuse to try some cool new technology that will look good on a resume. In two of them, they were paid the going rate. If you're not getting paid, or getting paid a stipend, then it may be fair to use the start-up as a sort of experiment - the cool experience may be all you get out of it - but this should at least be agreed upon. However, if you're getting paid the going rate, then this is a job, not a party, and your job is to get the job done. Lets be honest, this sort of thing goes on at large companies too for two reasons: resume stuffing, and job security code. My favorite is when someone builds some really "cool" tech that only they understand, uses it to get a new job, and then quits. If a manager lets this happen, they ought to be fired too, in my opinion.