So, on my Mac:
11" Macbook Air, 4GB RAM, 120GB SSD, Mac OS 10.7.3
I can successfully log into the Gehn Shard, however after login, all I see is a blank screen. It's an empty black window that says Uru - Gehn Shard.
The only thing that happened between when it worked and didn't is that it updated itself, however I hadn't logged in for a long time anyway, so that isn't necessarily the cause.