I recently added a second monitor to my Mac. I'll see what I can do to make PM more second monitor-friendly.
IMHO, one of the best things that could be done "to make PM more second monitor-friendly" would be to make the Preview window non-modal. Currently (at least in the Windows version), I can move the Preview window to my second monitor, and it will remember this positioning the next time it is opened. However, it should be non-modal and allow for the following...
(1) Changes to color-class, star rating and tag status should be reflected in the contact sheet when made in the Preview window (and vice-versa).
(2) There should be a toggle-style option that would "link" the currently selected image in the current Contact Sheet and current image in the Preview window. When this linking is enabled, as one steps though images in the Preview window the selected image in the Contact Sheet should change. Likewise, select an image in the Contact Sheet and the Preview window should jumping straight to that image. We could easily use full-screen mode for the Preview Window and select the image to review with the Contact Sheet. Making this "link" optional should avoid problems with the standard behaviour of the Contact Sheet that allows selecting multiple images, etc.
-Ian