This is a very nice idea. The help is good and readable.
It could be improved however. Suppose after you generate a plot, then after the fact want to use this tool? You can't do so, instead you must recreate your plot using this tool. A better approach would be to allow this to work:
h = plot(rand(10));
overviewPlot
Also, these variants should work too:
h = plot(rand(10));
overviewPlot(h)
plot(rand(10))
overviewPlot(gcf)
Finally, I note that rotate is disabled once you do the overviewPlot.
