I ran a .NET app from the Internet the other day - Internet - Code Access Permissions - from Chris Sells' site (just click on the link if you have IE6 and .NET runtime installed). This impressed me, mainly because it was the first time I had done this and it also made more tangible the promise of downloadable .NET apps with rich UI's and no client installation hassles.
It led me to experiment with the sample XML-RPC.NET client apps to see whether the library could be used with a downloadable client, the sort of thing you might want to do, for example, if you were providing a .NET Blogger API client.
As a guide to fiddling around with the security settings that are necessary to allow the XML-RPC.NET library to call out to an XML-RPC server on the Internet I found this article by Saurabh Nandu very helpful.
I placed the MathApp sample on two sites:
MathApp 1 - http://members.eraserver.net/cookcomputing/mathapp.exe
MathApp 2 - http://www.cookcomputing.com/mathapp.exe
And used them with the instance of the MathService XML-RPC server running at http://members.eraserver.net/cookcomputing/mathapp.exe (this is the default URL when MathApp runs).
Following the example of Saurabh's article, I experimented with various levels of security. For example, giving them the Medium Trust security level (one level less than Full Trust) meant that I could make XML-RPC MathService calls from MathApp at Eraserver but not MathApp at CookComputing - because this level allows a downloaded app to connect only to the site from which it was downloaded