The new feature I mentioned this morning is done. Now, in addition to the "where was this posted" button on the footer, you will notice the entry's time zone. Each entry can have its own time zone—in addition to the site-wide default.
I still have to fix a couple of things related to this change, like the fact that the date headers ("Thursday 24 November 2011," just above this entry) are on UTC rather than local time. But going forward (and going backward if I ever get supremely bored), you can now see the local time wherever I was when I posted.
Incidentally, if you want to bring the tzinfo database to your .NET application, I have licensing terms.