This plugin is very useful, however I just want to alert Keith and users that if it's used in conjunction with Infinite Scroll, Permalink Finder will keep appending posts to the end of queries, with the effect of padding query results with an unlimited number of unwanted and seemingly random posts, after specific parameters of the query have been satisfied.
For example, if you search for August 2012 post, with infinite-scroll and permalink finder installed, you truly will get infinite results! Permalink Finder will continue to suggest posts that might suit the query (but don't) instead of returning the 404.
This is of course part of the design of Permalink Finder, but Infinite Scroll depends on getting a 404 at the end of a loop in order to know when it has satisfied the results of an archive query. So, in this case, the extra posts appended by Permalink Finder at the end of the query become an unwanted feature.