Calling Trello "bootstrapped" feels a little disingenuous. It came out of Fog Creek Software, who had all the necessary people on payroll already. As far as I understand it was a side-project in an otherwise profitable and long-running company, that eventually got spun out with dedicated resources. When people think of "bootstrapped" startups, I think it's most natural to think of a team working for little to nothing, needing to become "ramen profitable" ASAP, and not having the safety net of a stable job, free food in the office, legal/marketing/HR and other support services, etc.