WordPress.com Stats is the analytical software which helps bloggers on WP.com hosted blogs. It recently underwent a revamp in design-
Note a simple change from Line to Histogram charts, and added Tabs can add so much value to data.
However WP.com really needs to addin Geo-Coded Stats (Visitors from where) and Some level of Campaign Tracking (similar to Goals in Google Analytics)
Earlier WP Stats
Now WP Stats