Didn't apply (from a Hubspot office ex-USA) but had been approached on LinkedIn by a Hubspot recruiter, was who very nice, helpful and supportive.
There were 4 rounds, the first of which was with the recruiter, covering motivations and other ex-professional achievements; round 3 with another manager; and round 4 was with a few directors.
Throughout the interview process, there were questions related to knowing the product, the competitive landscape, your self awareness, motivations, and cultural fit. It seemed pretty clear that Hubspotters are infectious, people who are ready to engage and get a conversation going.
Some questions that were a little different are rather common in the tech industries (teach me something) or related to Inbound Marketing, so read up and know your stuff before attempting any round.