I had just completed installation of .NET RTM this morning on my dev machine and was about to build and test the XML-RPC.NET samples when I checked my mail and discovered that JT Perry had beaten me to it. JT confirmed that the client code worked fine under .NET RTM.
I had problems getting ASP.NET to work. Event Viewer had this event:
aspnet_wp.exe could not be launched because the username and/or password supplied in the processModel section of the config file are invalid.
I changed the username in the processModel section of machine.config from ASPNET to SYSTEM and everything started working again. Probably not recommended on a production server. When I get the time I'll fix the problem properly.
I'm planning on making some further changes this weekend and plan to put a 0.4.2 RTM-compatible release on the website Monday evening.