Function traces log every include, function call and method call to a file. If the xdebug.trace_format setting is set to "1" then the trace file is an easy-to-parse tab separated format. The information that is logged includes the time-index when the function started and ended, and it also contains the amount of memory that was in use when entering the function, as well as when leaving it.
He's written up a sample script (you can grab it from the Xdebug CVS server) that you can run on a file and push all ouf the output to the trace file for easy parsing. The script reads in the file and displays the results in a nice format on the command-line (easily adaptable for a web frontend).