I was writing a quick script today to clean up some data for an import using Coldfusion 8.  It runs a single query and then loops over the results updating a different table.  Now before you roll your eyes I know this is not the best way to do this, but I needed it done quickly.  When I would run the page it would stop with a 500 Heap space error and Coldfusion would die.  I couldn't figure it out so I decided to try it on a development copy of Railo.  The page didn't finish, but I got a Debug out of memory error.  Which pointed me in the right direction.  I added in <cfsetting showdebugoutput="false"> and the page ran perfectly in Coldfusion 8 and Railo.

This is a good reason you should never have debug turned on in Production :).  Extra kudos for the Railo guys though.  Railo stayed up and working and also give me the debug information I need to figure out what the heck was going on.