When a Query object is created, DatabaseMap#getTableByPhpName() is called to autoload the related TableMap class. The method initially tries to load a namespaced version of the file, searching for a \map\WateverTableMap class. Because the class doesn't exist (sf1.4 projects don't normally use namespaces) this triggers sf1.4's AutoloadAgain autoloader in dev environment, which in turn rebuilds the entire autoload cache.
And this will be done for every unique query class instantiated for a particular request.
Any ideas on how to mitigate this?