I ~want~ to use Meteor on a large project, but they only are in Preview and in the FAQ states there will most likely be major API changes each [preview?] release, with no 1.0 release date in sight.
[meteor dev here] The latest plan for 1.0 is at http://roadmap.meteor.com/. It's too early to have a specific release date but it'll be well under a year from now.