I ran into an interesting problem with .Net 3.5 today, when trying to access response headers like so:

context.Response.Headers.Add("Content-Disposition", "attachment; filename=\"" + filename + "\"");

The application returns the error "This operation requires IIS integrated pipeline mode." Through some quick googling, I discovered that the problem existed in beta, and apparently wasn't corrected for the release.

Interestingly, there is a simple workaround for adding headers:

context.Response.AddHeader("Content-Disposition", "attachment; filename=\"" + filename + "\"");

Why this simple change works I have yet to discover, but until Microsoft gets a patch out that corrects this behavior it'll do for me.