On a somewhat lighter note, after the serious entries of the past week, this is the start of a thread on soc.history.what-if in which James Nicoll starts speculation about what would happen if the US in 1958 found a doorway in time to the Earth of 250,000,000 A.D.. This evidently fired the imagination of the posters there, as there is quite a lot of good, interesting speculation throughout the thread. Even though I like blogs quite a lot, Usenet still beats them when it comes to sustained discussion like this.
Related links:
The Epona Project, an attempt to create a believable extrasolar in detail.
One view of Earth 250,000,000 A.D.
The Future is Wild, the website of the tv series of
that name, which explored a similar issue. Heavy use of Flash.