As @Brogan said this is coming in the next release (1.2).On this site if you put a member's name in a message with '@' before it, that member's name becomes clickable and, when clicked, the black pop up window opens up. But, on my site at www.gdf.tv when I put @ before a username it does not become clickable?
How to fix or activate this?
Xenforo are currently testing the next realease (1.2) here at the xenforo.com site, to iron out bugs and prepare it for beta release to customers.
You'll find the '@' and a number of other features currently rolled-out here that you won't be able to use on your own board yet.
An announcement will be made once 1.2 beta becomes available for download.