Hi,
I've just been attempting to try out the new addons stuff released as a live beta with 1.5.
If you follow the instructions found on the Rift forums etc... they direct you to click 'Addons' > 'Open Addon Directory' from the character selection screen to get to the location that you need to place any addons.
On OS X Lion (10.7.1) and CXG 10.1.2 this causes the game to crash every time. It looks as though its a crash related to Explorer.exe attempting to open the folder.
You can manually install the addons in the folder and they work fine. My addons folder location was here:
~/Library/Application Support/CrossOver Games/Bottles/RIFT/drive_c/Program Files/RIFT Game/Interface/Addons