I'm looking for a book (or web tutorial) on Ajax with a strong emphasis on the server side of things. I'm already comfortable using jQuerys various Ajax related functions, but I'm sure my server-side code could be a lot better. Sometimes I return HTML and sometimes I return JSON. I've tried various techniques but I'm not convinced that I'm doing things the "right" way.
Most books seem to emphasis the client-side of things. I've been browsing Amazon and it's not always clear which focus a particular book is taking.
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." -- Ted Nelson
I know of no books on Ajax per se that emphasize the server. But's that's not really what you are asking about. How the server code is written is actually pretty moot; what's germane is the API that the server exposes.
Perhaps what you really want to delve into is RESTful web APIs?
P.S. I don't see any issues with sometimes returning JSON and sometimes HTML; I do it all the time. It depends upon usage and the needs of the API.