I applied online and fairly quickly had a telephone interview (as I explained I had other interviews in progress). I was then called in for an extremely efficient stage of 3 interview rounds in one go. An interview with the CTO and a Product Manager (for which I had prepared a case study presentation), then with the Engineering Manager and an Engineer, then finally with the CEO and another Product Manager for cultural fit. I was informed beforehand that the interview may be called short if I didn't proceed through to the next round; fortunately I proceeded through all stages. There was a final phone call the next working day to clarify a few issues, and then an offer was made that same day.
I found this an extremely efficient way of interviewing, effectively getting a few of spread out interviews into one intense afternoon.
Through the interview process I got to ask all of the questions I had, and I got a really good impression of the team and company as a whole.
I would highly recommend interviewing (and working) at HubbleHQ.