So the current behavior of two equal dates being considered not-equal is as jarring as your counter example of two non-equal dates (different timezone) being considered equal.
Indeed!
There doesn't seem to be an easy, direct solution because I'm assuming we don't have a primitive for "the offset at this location on X date in the past". So the next best thing might be a PlatonicDate (obviously a name-in-progress :)) that represents the abstract idea of a Date without regard to location, and then an object to connect a particular place/offset to that concept (but the second one would have the same problem as we currently have).
Well, for me at least, the solution we chose for Squeak has been working well. Here's the main discussion:
http://lists.squeakfoundation.org/pipermail/squeak-dev/2012-February/162872....