interactively getting z-value on a pcolormesh


I often use mpl interactively (in ipython --pylab) to plot 2d data on
basemaps using pcolormesh. When moving the mouse over the map, I can see
x,y coordinates being displayed in the bottom right of the plot window.
What would be more interesting for me is the value of the pcolomesh'ed
data variable at the point where the mouse cursor is.

Any way I can get this information?

Cheers, Andreas.