While we're not a big startup, we are using Meteor in production (https://www.getsubcurrent.com).

We picked it because it enabled us to move much faster than anything we had used in the past and while it has issues that I foresee being problematic, it seems premature to optimize for them. The Meteor team is doing a great job maintaining compatibility and not forcing us developers on to make any changes to our apps as they're rolling out exciting new stuff. Granted, I did jump on when the platform was (relatively) mature late last year.

Very happy with decision so far and looking forward to building more stuff on their platform!