When installing a NuGet package to a new Xamarin.Android project, VS hung for several minutes. I broke into VS with the debugger and found via the callstack (attached) that the hang is caused by the NuGet package manager enumerating references, causing the C# project system to request a synchronous design-time build on the UI thread, leading to MSBuild running a Xamarin.Android task. The Xamarin.Android task downloads many megabytes of data from the Internet. This seems very inappropriate for a design-time build, which is supposed to run in under 200ms. Please adjust your Xamarin.Android MSBuild targets to skip expensive tasks like this during design-time builds!
Can someone at Xamarin please a bug to track this and link to it from here?