But my personal experience says Lambda is ready for prime time. We use it in production. ~15 million API calls per day. Mostly user facing HTTP requests. Even with the rough edges I would prefer to use it for any new web development project. It feels like at least an order of magnitude reduction in risk/complexity of scaling and deploying code. Its not "zero" but that is huge for me and for my team. We spend more time shipping.
[1]We wrote one: https://github.com/bustlelabs/shep but there are plenty of others mentioned in the comments.