If you ever have to add a Service Reference for the SharePoint List WCF Service to a project in Visual Studio 2010 you may encounter a "Bad Request" or "There was an error downloading ..." type message even though you can view the results of the same service through a browser.
The way around this is very simple and resolves the problem, however, in my
mind, this should only really be done on development machines to get around this
issue and not rolled out across a Live installation. What you need to do is go
to IIS and change the authentication methods for the _VTI_BIN folder to disable
Anonymous access. That's it. You can then successfully add the service