Did you know you can sort your photos in Lightroom by Edit Time? In the Library Module there is a very useful sort option called Edit Time. Sorting the grid view by Edit Time will display the thumbnails with the most recent ones at the top of the grid.
This is an easy way to select all of the photos that have had any form of editing applied. Note that adding keywords counts as editing.
For more information, sign-up for our Lightroom workshop on January 19, 2010 from 6:30pm to 9:30pm.