Well to start with, they went to MacWorld and previewed the app there. I don't follow the space much, but I think the company was somewhat well-known already for Mac apps.
We debuted the app at Macworld. Our Clear coverage was in a MacRumors post that covered highlights from the show floor.
Our marketing was definitely competent. Realmac Software worked with a local video producer and shot a great sizzling video, and we reached out to a bunch of people with the beta and promo codes before the app hit. But there wasn't anything special or crazy going on in the external marketing.
I can't stress enough, the answer to the submitter's question is the app, and what I would describe as a design and feature reboot to a very crowded space. I think this resonates with iPhone users.
The app got people who saw it and tried it very excited. It sells itself, and seems to make evangelists out of its users. Sure, our marketing and press efforts helped accelerate its spread through twitter and stuff on launch day. But as a random anecdote, we've had thousands of people send out copies to friends as gifts already, and I've simply never seen that before.
If we're onto something here, it's definitely with the app and its design and not so much its marketing. Clear's marketing is very vanilla. Its design, not so much.