Ditto: so much about Meteor just makes the day-to-day work of building something a real pleasure compared to other tools.
For me, the thing really holding it back from more serious work is that I've had real problems getting testing to work well: Velocity[1] has had a bunch of problems for me.
I hope things like the focus on MongoDB and the lack of good automated testing tools are just because Meteor is still fairly immature. It could be a really good tool for a lot of use-cases.