Is Mercury completely mapped?

[ar81]

Planet surface we have is one half of the planet surface.
I recall a probe was sent to take photos of the other side.
What do we know about it?

 

[FordPrefect]

The first flyby of Messenger resulted in lots of never seen before hir-res images of Mercury. Though there is still approximately 20% of its surface not yet mapped.
For more information visit the missions homepage:
http://messenger.jhuapl.edu/index.php

The next flyby is scheduled for October 6th, expanding the global map coverage.