Most reliable way to mirror large number/size files/folders between drives & computers Often I find myself shuffling large directories (20 GB+) of data between computers or drives.  What is the most reliable way to ensure that all data is being exactly mirrored with permissions/dates intact?

Bonus points if it's wrapped in a GUI rather than a terminal command.

I saw this question regarding copy utilities for OS X, however the answers were skewed towards speed.  My concern is ultimately file/data integrity.
rsync has proven to be very stable and effective throughout its years of Unix service. It’s included in any OS X since Tiger and it’s relatively easy to use. 

If you want the bonus of a GUI, you can use Arrsync, a free utility better described as: 


  A Mac OS X graphical front end for the utility rsync.


If, on the other hand you want something more “easy to use” I can recommend you take a look at the two winners:

SuperDuper! ($)

Carbon Copy Cloner (Free, Donationware).

Either will allow you to clone entire drives or folders or anything you can imagine. 

Their reliability to copy permissions, ACLs, and that stuff has been proven throughout the years.