It's supposedly updated daily, but that's probably only the satellite images.
The aerial photography is either the same stuff as google earth's or slightly newer. Though I haven't used it in a few months since it developed a bad habit of crashing whenever I zoomed out.
The maps of massachusetts are older than Google Earth's right now. Google Earth was updated a couple months ago with "new"er maps.
powerkok, check out http://local.live.com if you haven't already. A lot of places have the "bird's eye view" available. That shit is fucking amazing. When in bird's eye view you can view things from 4 different angles, too.