I was looking for a quick way to rotate only the even numbered pages in a document that I had scanned in using my Brother MFC's scan-to-email feature in duplex mode -- I found that it had flipped every second page, and they needed to be unflipped. It turns out there's a not-so-obvious way to do this rather easily.
Make sure the sidebar is showing on the side of the document you want to work on in dual column mode (Control-click in the Thumbnail column and select Columns » 2 Columns), and you will see that all the even pages line up in one column. You can then drag a square around the entire column, and keep going down until you've highlighted all the pages you want to rotate.
Next, press Command-R twice to flip the selected pages upside down, or once to rotate them to landscape mode (90 degrees). This works pretty much as it does on a single page. There is a also a menu command to rotate pages if you don't like using keyboard shortcuts.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20091110000935690