Just a heads-up for anyone who happens to use this recipe: I am aware of a compatibility problem with Mac OS X 10.8.3 (the format of the bookmarks file that stores Reading List items has changed slightly).
Update: I'm not sure if the problem was actually introduced in 10.8.3 or if it was simply a circumstance I hadn't encountered before, but in either case, I've update the recipe with a fix. (Basically, the reading list bookmark's date can be found in two places, but I was only looking in one place; now I check both if necessary.)
https://github.com/anoved/Safari-Reading-List-Recipe