And I sure listened.
The night consisted of several seriously cool demos, and included a bit of history on how IL evolved. (I'm a sucker for computer history stories.)
Apparently, IL is the grandchild of the metadata format used between the Microsoft C++ front end and back end compilers. The Microsoft C++ frontend compiler compiles the C++ codestream to an intermediate format, and the backend compiler converts this stream into plaform / CPU specific instructions.
IL is based on that intermediate format, though it has been changed somewhat from its original form.
In the CLR model, the backend compiler is now the JIT compiler, and the JIT can make even more aggressive optimizations than a traditional compiler.