Nice plugin, will test it tonight! :-)
What I've been doing sofar is: putting up a new wordpress installation, then used category as geographic marker, tags as what companies specialize in, and "geo mashup" plugin to display the address in a Google map - displaying posts as information for companies using permalinks.
What I miss in this solution is an ability to have a map with all companies displayed in one single map with links to each company-page, as well as having a more respectable main page than all the recent posts...
Now lets check out this newplugin..