Is there a performance advantage using ATL for a Web Service over .NET?
If no issues exist with using unmanaged code and the .NET Web Service is all managed, there are minimal performance differences. However, the first time a .NET Web Service is used, loading the .NET Framework does take longer for the initial response from the Web Service. Using ATL, this is not an issue, and the first use is very responsive. ATL will have some performance advantages over the .NET Web Service. The bottom line is this: Performance shouldn't be the deciding factor in determining which way to write a Web Service.
Why doesn't my ATL Web Service show up in the Add Web Reference dialog when I select the hyperlink to see my local Web Services?
Because the default .vsdisco file that Visual Studio .NET creates in your Web root does an auto-discovery for Web Services, and it only looks for other .vsdisco files. It doesn't look for .disco files (which is the file extension that an ATL Web Service has). You can manually change the .vsdisco file to explicitly reference your ATL Web Service if necessary, or you can directly reference it as you did in today's lesson.