I think that it's a difficult question considering the sheer size of ASP.NET and the Framework itself.
However, saying that, I'd be keen to discover best practice solutions for data access solutions, such as:
- Master-Detail views
- Paging records
and only retrieving the requested
data from the backing store
- Displaying hierarchical data in a
grid
- Loading and saving images
- Editing data 'live' on the page without postbacks
These are the sort of queries that I see on sites such as this one again and again. I realise that your book isn't a 'cookbook' of solutions, but it would be useful if these not-so-esoteric topics were touched upon. Of course, I'd expect that Dynamic Data, MVC, Routing and so on would also be discussed in depth.
Also, AJAX is still very relevant, but I'd argue that AJAX.NET may be on the wane. What about some info on adding AJAX functionality using jQuery, which is going to be officially supported in v4.0?
I'd rather code samples be in a single language, as it's easy to convert from one to the other and it saves on trees :)