Can you point me in a direction to get started?
What exactly do you mean by server-side processing? I call .net restfull web services all the time from JS that return data.
What specific questions do you have? What do you want to use .NET for?
OK, like I mentioned earlier I do that often in my apps. So what are you looking for specifically? Do you already have a web service for this?
Yes, I have a mapservice and a page setup that has an identify button that returns feature attributes from a polygon coverage. I would serve it out to you but IS has keeping it inside our domain for now.
So do you have a RESTful web service or a SOAP web service that does the database searching?
According to ArcGiS Server Manager the service has both REST and SOAP capabilities.
This topic is getting a little confusing then. If you are talking about querying data from ArcGIS Server then of course that will work and there are many samples in the JS API for doing this. I thought you were talking about data that resides in a database that was not Geo data (such as ArcGIS server). Maybe you need to clarify your requirements and workflow.
Retrieving data ...