exponential notation in axis lost?

Dear all,

I am producing some plots and in many of them I have in the y-axis typically

0.00001 0.00003 ... 0.00009

In previous versions of matplotlib this would go into a

1, 3 .... 9

and then a x10^-4

close to the top. This was very nice.

This feature seems to be lost, at least with the defaults.

How can I reset this?

I would also like to know how to specify the number of ticks to be
used for an axis.