Another Microsoftie, Josh Williams follows my blogs and pointed out another case where a base address matters: NGEN.  When you NGEN your assemblies, the new images are loaded at the same base address as the original binaries.  As Josh pointed out to me, NGEN images do have significantly more relocations (similar to a real native image), and on 64-bit platforms may end up using an extra jump stub when they get rebased far away from the call targets (i.e. when a 32-bit offset no longer works).  The relocations will affect load time, but the jump stubs will  affect runtime performance.

--Grant