[kls]

You would have saved a lot of time and frustration by building the single page app first and putting analytics on it to see how many non-JavaScript clients you where getting (most are surprised at how few the number is) and then if the number justify it, build out an older style UI separate from the modern web app that just proxies data to the same REST services, then use a sniffer to decide where each client goes. This is a simpler solution than trying to layer on dynamic functionality while trying to support the least common denominator. 9 time out of 10 though, when faced with the decision, the effort to chase older browsers is better spent chasing a larger market like Mobile.

[Lazare]

I know! :( It was definitely a learning experience.

And in regards to your comment on mobile: Agreed! Not only is getting a slick mobile client a much more important use of resources that stuffing around with progressive enhancement, but a good JSON/REST API is really really helpful when it comes time to get a mobile app working.

Thinking of webapps as client-server applications communicating via a JSON API is really helpful at the moment, I think.

[kls]

Yes many people make that leap after a first iteration, but once you do the pattern becomes very clear and very powerful. Looking at your back-end as a platform for all future clients really helps as well.