Mapping Center Answer:

While we have not done anything new in terms of making fancy swoopy arrows and such that was referenced in "Making Maps that show Flow From Place to Place", we have added functionality that provides some alternative ways to show change over time.  Specifically time aware layers can be used to show movement from place to place, provided your data have either a date/time field (snapshot), or a start and end time field (duration).  

This new functionality could be combined with what was in the blog entry to make a much richer experience.  For instance the arrows I was showing in that blog entry represented phases of a battle.  The timing of when the arrows were meaningful was not exactly simultaneous, and there were three phases to the battle.  By creating more arrows and setting them to have a duration, I could animate that map and make it a more effective presentation.  In fact the map I made was an incomplete presentation because I could not overlay the additional phases of the battle and so I settled for showing just the 2nd phase.