I applied through referral (certainly very helpful to know someone there). First step was a call screening. It was a very simple, informal conversation, basically just making sure you are interested and know what the company does. Response time was within 24 hours, and I got called back to come down to the New York office in person. This was much more of the typical character test and seeing if you would be fit for the position. I talked to two people, and the process took a little more than an hour. Questions were general, nothing too challenging, no brain teasers. The people were nice and friendly, and they definitely are trying to see if your personality would be a good fit within the company.
My best advice would be to be yourself and keep it conversational: a good portion of this job is effective communication, so demonstrating that you can carry an intelligent conversation about digital advertising while not being a brick wall of a person definitely can set you apart.
After this, they reached out early the following week requesting references, and I got the offer before the end of that week.