My team has been using Lambda/Dynamo/API Gateway/Cognito for a couple of web services this year and really loving it. The addition of CloudWatch Events to the mix was really the final piece of the puzzle for us, because now we can launch lambda functions on a schedule to perform asynchronous background tasks (think data crunching, email notifications, etc).
Lambda is maturing so fast that I almost feel bad complaining about it, but of course we have run into our fair share of issues, too. One thing that's making our life more difficult right now is the fact that when you launch a Lambda function in a VPC via CloudFormation, the function's ENI doesn't get attached until the function runs the first time, so CloudFormation doesn't know anything about the ENI. Thus, when you tear down the CF stack, the ENI gets orphaned and hangs around in a detached state. Throw some automation into the mix and you can start eating up IP addresses in your subnet really fast. I have no doubt they will fix this soon.
Lambda is maturing so fast that I almost feel bad complaining about it, but of course we have run into our fair share of issues, too. One thing that's making our life more difficult right now is the fact that when you launch a Lambda function in a VPC via CloudFormation, the function's ENI doesn't get attached until the function runs the first time, so CloudFormation doesn't know anything about the ENI. Thus, when you tear down the CF stack, the ENI gets orphaned and hangs around in a detached state. Throw some automation into the mix and you can start eating up IP addresses in your subnet really fast. I have no doubt they will fix this soon.