I got in touch with them via a friend that did an internship there. Getting through to the actual interview took a while, with some folks not responding for prolonged periods, but eventually I got through. From that point on, my experience was *fantastic*.
They did an online coding challenge which was very simple. Two questions, the first trivial and the second a bit harder, but involving palindromes and should be pretty easy if you can do normal technical interviews.
Then they brought me in for a short in person onsite where I had three (only three!) interviews with folks of varying seniority (from mid to pretty high).
Upon receiving the offer they made it very clear that they were going to be very flexible with it to allow me to succeed within the company. They're so focused on individual (and group) success, and it really shows throughout.
Honestly, I enjoyed this interview process and the negotiation process more than any other company I've ever applied for. HubSpot really stands out in a lot of ways.