In my next column I'm writing about how to deal with problems when calling Web services from .aspx pages. Some of the technical content for this article is based off information that was provided by Lance Olson, a program manager in the XML messaging group here at MSFT. In particular he points out the use of an event handler that I had never heard of or noticed before. The trick is to add your event handler using the AddOnPreRequestHandlerExecuteAsync() function. If this works as planned (and I expect it will ... I haven't written the code to test it yet) it will allow your event handler to get called before a thread from the process thread pool starts handling your request. Why is that cool? It will functionally allow you to do HSE_STATUS_PENDING request handling for aspx pages.
That sound you hear is all the down and dirty ISAPI programmers drooling.
Of course the async web method support is a lot cleaner, but this will work for aspx pages (or any asp.net request for that matter).