So I upped the limit to 128 MB, but still get the Fatal error.

The most recent was here:

[Wed Jun 06 06:21:07 2012] [error] [client X.X.X.X] PHP Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 15851277 bytes) in /my/path/to/ubbthreads/libs/ubbthreads.inc.php on line 835

Line 835 happens to be the return from function graemlin_url:

PHP Code
return preg_replace( $patterns, $replaces , $output );

Any other ideas?