Well ~~~ I don't know if I did this incorrectly or not but it is working the way it should
I'm running a MacBook Pro 17", Lion OSX
I opened two finder windows side by side. Accessed PS CS5 and the plugin folder in one and the PS CS6 plugin folder in the other finder window. In CS5 I duplicated the Plugin I wanted to move and then dragged and dropped into the CS6 folder.
Everything works fine for me as it did in CS5.
FWIW my Plugins are Nik CEpro4, Dfine, Sharpener Pro, Viveza 2, HDR Effects Pro, Silver Effects Pro. Along with Topaz Adjust, Detail, In Focus, Star Effect and Imagenomic Portraiture and thee from Flaming Pear.
I haven't run into any hiccups yet. But........Got my fingers crossed.