Just downloaded the trial version of Microsoft Streets and Trips 2009 and compared the map for Calgary Alberta (a fast growing city) with S&T 08 to see if upgrading would be worthwhile but found no changes at all. Then compared the map files and found the same file sizes and creation dates in both versions (eg. USA CD - 603,829 KB & date of 1/9/2008 09:11)! Similar for "USA HD" and others...
Now, I have noticed others commenting on map additions (Mexico and Ladysmith, BC IIRC) so cannot quite figure out what is happening here.