STOP THE PRESS: All users of Macs and Pc's, Read this.

When performing a folder replace:
1. Pc's MERGE the contents of identically named folders.
2. Macs REPLACE the contents of identically named folders.

Bigtime difference between the way Pc's and Macs operate! It took me a while to realize this, but if you're replacing folders on a Mac, it does just that - REPLACES the folder (and its contents) whereas if you're replacing folders on a PC it MERGES the contents of the folders and only REPLACES files with the same names.

This is what I was accustomed to and expected, so you can imagine my surprise when I dragged a folder with like, ONE file in it to a directory with the same name folder in it, but with a gig of stuff in it and when it replaced, all that info disappeared!
(to Apple's credit, they do say "an older item with the same name already exists in the location... are you sure you want to replace it with the newer item?"

so to sum up, be careful! Macs operate differently to Pc's in this case.
(I actually prefer the PC case)