Eric's review is detailed and covers Sleep Monitor's capabilities well. I was pleased to see the AppleScript interface provided an answer for one potential short coming.
One aspect Eric raised was the missing ability to export your data. This is possible to do with Sleep Monitor; you can export all your gathered information using the
File > Export… menu item. Sleep Monitor can export your data in RTF, plain text, Word, and XML formats. The plain text export is tab separated, so can be imported directly into a spreadsheet.
A free 30 day demonstration of Sleep Monitor is available to download and try now.