I just read 20+ pages about this on QJ. And from what I understand:
This was originally made for 1.5. People have been using 2.5 top_menu.rco files to flash this on OE firmware... But if you do, there will be some missing icons on your XMB. :(
When, and if they can decrypt the 3.0 top_menu (this confuses me, b/c I thought 3.0 was decrypted awhile ago...) than this could be used on OE, without losing icons. Hold on, I'll find the link so you guys can read for yourselves.
EDIT: OK, here's the release thread. So yes, this has been done on OE firmware, but like I said, you'll be missing some icons.
CUSTOM ICONS WIP/RELEASE THREAD