Posted to his blog, Dave Marshall has a tip that uses declare and a trick or two to check out the memory usage of your scripts.

As far as I know, there isn't any memory footprint profiling in Xdebug, I think there was at some point but they removed it because it was a little flaky. I like to monitor the memory usage within my scripts, and I've found this simple snippet can help.

The script defines a log_memory function that pushes the memory and time information into a session value. The register_tick_function method is used to add log_memory to the handler and its called over and over from inside his for loop.