Cons are the normal flip side of start up benefits: Some long hours, internal processes still being invented, the need to be comfortable moving full steam ahead with uncertainty, that kind of thing. You either love it or you don't.
Weirdest con (is it one? I almost put it in pros.) is that we have so much opportunity as a company that we have to say no a lot, and it requires discipline to not get distracted - we're doing well, I think.