Thank you for writing this plugin. It works perfectly with WP 2.7.1 and Atahualpa 3.3.3. I was beginning to get a LOT of revisions and had tracked down the wp_config.php tweak for posts ... but this is much better.
One note that should be added to the description somewhere, though, is that after you install it, if you go into a page or post and do an Update, because WP just did an auto-save for instance, the plugin will delete all revisions greater than the count set for the page or post.
I wasn't expecting that. I figured I'd be deleting all of the old revisions by hand so I hadn't done a database backup yet. ... My bad.
It turned out okay, but a note about the "automatic" nature of your plugin would be nice.
Other than that minor doc tweak, great plugin! Thank you!