Obviously an easy fix here, but created the bug because I don't know whether Jeff wants to keep the memory tracking in permanently, or if that was just meant as more of a dev/debug thing.
Solutions:
A) update documentation and environment checker, OR
B) remove calls to memory_get_peak_usage().
Workaround:
Edit cerb4/libs/devblocks/Devblocks.class.php, line 713 and change
self::$start_peak_memory = memory_get_peak_usage();
to
self::$start_peak_memory = 0;
Edit cerb4/plugins/cerberusweb.core/classes.php, line 213 and change
$tpl->assign('render_peak_memory', memory_get_peak_usage() - DevblocksPlatform::getStartPeakMemory());
to
$tpl->assign('render_peak_memory', 0);
Bug
Closed
memory_get_peak_usage() funciton requires PHP 5.2.0, docs/installer only require 5.1.2.