At the moment, a new instance of the CLR is used for each explicitly
invoked application, although services may well share a single CLR (I
don't rightly know, to be honest). I would expect this to change over
time though - one of the reasons for the whole AppDomain business is so
that a single CLR *could* host many different applications.

Actually, the CLR is not really managing applications, it just creates a VM environment within a Win32 process for managed code. The
CLR is loaded and initialized at application start-up time, that means that each managed application process has his own copy of the
CLR loaded.
Note I'm talking about current supported versions of the OS and CLR, it's possible that upcoming versions of Windows OS could move
whole or a part of the CLR to OS space.

Willy.

Each managed application will loads its own copy of CLR. Sharing of CLR is
done at OS level (basically LoadLibrary()).