Kevin and Julia Hartz of Eventbrite believe that having a compatible relationship with a co-founder is paramount — whether it’s romantic or not. And it just so happens that the startup part and the marriage part are both working out pretty well for them so far. They raised $60 million in April at a valuation of somewhere between $600 million and $700 million, giving them some flexibility on timing for a much-discussed Eventbrite IPO. It probably helps that they don’t argue over who gets to drive.