I feel out of my depth almost every day, and I love it.
Working in a company where you're the most senior developer is only fun for so long. Eventually you'll come up against a problem you'd like some guidance on, or you want someone to challenge your ideas.
At Datasift, I'd go so far as to say that everyone has more experience than me. They know the code, they know the problem domain. They know why things that I think are a mistake are actually the correct way to do things.
Every day I learn something new. It might be about ZeroMQ, it might be about long running processes in PHP. It might even be something new about Jira, our bug tracking software. No matter what though, I always learn something new.
So, embrace being the dumbest guy (or gal) in the room. Treat it as a chance to learn more. Treat it as an opportunity to take your understanding to a higher level. Feeling out of your depth isn't a bad thing, it's a necessity.