I received initial communication back from Tumblr on the second business day after submitting my application online, wherein we setup a time for an initial phone screening two days later. The initial phone screen went very well. The recruiter was very pleasant to speak with and the conversation flowed quickly. The phone screening took about 15 minutes and covered the basics including, desired salary, work experience, why tumblr, and when I'd be ready to start.
I shortly received another email from tumblr asking to setup a technical phone interview and the following week I spent about an hour on the phone with one of the engineers. The engineer was surprisingly very patient and even encouraging when I got stuck on one of the questions. We did basic coding challenge (brush up on basic algorithms) and it went very well. We talked a bit about some of the challenges I'd dealt with in past work experience and the questions went from mild to moderately difficult. Regardless, there were no tricks and the interviewer did a very thorough job.
I received an email from tumblr that same day, just a few hours after my technical phone screen, inviting me out to Tumblr HQ in NYC to do a round of in-person interviews. Since I wasn't located in NY they offered to pay for my flight and arrange for transportation. I flew out to New York city the following week and did about 4 rounds of interviews that lasted roughly 3 hours. I met with 7 different engineers/managers during that time. We did everything from code reviews to coding challenges, and architectural/design challenges. It was a pretty grueling 3 hours, to be honest, so be sure to do your prep.
Everyone I met with was extremely nice and inviting. The conversations were pretty casual and encouraging. I was offered cool Tumblr swag, free food and drinks. So overall my impression of Tumblr was pretty good.
A few days after my final round of interviews I got a phone call with a generous offer that included stock options and a signing bonus. I was very happy with the offer and accepted right there. I received a start date two weeks from signing my offer letter and relocated to NYC.