as MBlume mentionned[1], they seem to support NodeJS.
From the FAQ :
"At launch AWS Lambda supports code written in Node.js (JavaScript). Your code can include existing Node.js libraries, even native ones."
so it seems that you can avoid lock-in if most of your javascript code is not too coupled to Amazon's API
And they claim on the detail page:
"With AWS Lambda, there are no new languages, tools, or frameworks to learn. You can use any third party library, even native ones. At launch, AWS Lambda will support Node.js code, with support for other languages coming in the future."
Err, I think the parent's point wasn't lockin in terms of the code you write, but in terms of your architecture. Setting up your own system driven off of s3 or dynamodb events (if you wanted to move the functions onto your own bare metal) would be a pretty big project.
From the FAQ :
"At launch AWS Lambda supports code written in Node.js (JavaScript). Your code can include existing Node.js libraries, even native ones."
so it seems that you can avoid lock-in if most of your javascript code is not too coupled to Amazon's API
And they claim on the detail page:
"With AWS Lambda, there are no new languages, tools, or frameworks to learn. You can use any third party library, even native ones. At launch, AWS Lambda will support Node.js code, with support for other languages coming in the future."
[1] : https://news.ycombinator.com/item?id=8603059