I've been finding Proxima Nova[1] everywhere this year. I'm not complaining though—I think it's a beautiful, highly readable typeface.
Few years ago Mark Simonson, its creator, was the first type designer with balls big enough to let go of a tight control over PN's distribution and embrace its online use. Back then uttering "Cufon" or "embedding" on Typophile would give you strange looks at best and a flame war centered around lost profits and piracy at worst. He was also one of few designers to extensively hint fonts for on screen use _in smaller sizes on Windows_. PN was basically the first non-OS font that looked great on Windows in 11px. The last contributing factor was that in all caps PN looked very close to Gotham, but it was also few times cheaper. If you ever looked at Gotham, you know how well it works as a heading font. And PN was the only online-friendly alternative.
In other words, the position that Proxima Nova enjoys now is directly related to the liberal license that Mark released it under and the hard and focused work he put into polishing it for the online use. Props to him.
One of the things that's great about it is there are so many variations: Regular, Light, Regular Italic, Light Italic, Semibold, Bold, Extrabold, Black, Semibold Italic, Bold Italic.
Most other sans-serif typefaces we evaluated didn't have enough variation that it could reliably service any use-case.
We use proxima-nova on http://customer.io as well as in all our presentations (e.g. https://speakerdeck.com/sudonim/write-emails-people-will-rea... ) . Love that typeface.
And great work on the customer.io site! I was actually admiring it just yesterday after following your link in another thread: http://news.ycombinator.com/item?id=4912268
Just added customer.io too. ;)