Adam Wiggins, one of the three founders, was one of my favorite software engineering mentors back when we called it programming - as an example, he wrote an early rails plugin called "axeman" for the consultancy that would list controllers and actions by least-often-used, so that we could remove functionality that wasn't worth clients paying for. He also got me introduced to Vim, and another coworker there (Hi Simon Michael) demonstrated for me the orchestral nature of a true Emacs master operating at peak capacity, so I blame them to some degree for being stuck in the DMZ at the middle of the IDE war.
[1] The reason I know I was the first user was that in October 2008, Adam sent me an invite to try out Heroku and there was a classic rails error - they forgot to skip the before_filter for authentication on the "accept invite" controller and action. Bug quickly fixed, but definitely a funny anecdote. Even on day one it was obvious they were going places - I would have blind invested money into whatever venture those three were working on regardless of what it was.