I have used it extensively in several sites. The biggest application is for a New York ticketing site. I have marked 40 Broadway Theatres on individual maps, as well as another 40 or so tourist attractions. Each has its own map, and all appear on a big mashup map. I also have a traffic map for all of NYC. Everything works beautifully. I even made my own custom icons for this plugin. They are just transparent PNG files in a very easy-to-find folder. http://allticketsinc.com/
This plugin conflicts with another plugin: Google Street View. I am developing a site where I use them together. To do so, I have been forced to display the StreetView content within an IFrame, essentially having loaded it on a different WordPress Page with a custom full-page template. This is a little convuluted, but it works, and visitors cannot tell the difference.