mbrinson on "[Plugin: W3 Total Cache] MFUNC still not working"

Hallelujah! That worked for me!
@kokoschka - It looks like you're still leaving out the security_string part of the <!-- mfunc --> deal.

Here's what worked for me:

Added this line of code to the wp-config.php file in the root of the wordpress installation:
define('W3TC_DYNAMIC_SECURITY', 'mysecretcode');

Then used this code where I wanted the PHP to be run un-cached:

<!-- mfunc mysecretcode -->
  echo 'testing php execution';
  x = 10;
  echo x;
  whatever php code you want
<!-- /mfunc mysecretcode -->

Remember, the <!-- mfunc --> comments actually REPLACE the <?php ?> tags. Kokoschka appears to be including the <?php ?> tags within the <!-- mfunc --> tags which is not how it works.