Here's the method I successfully used to remove the "Unknown Location" listings on my vBulletin 3.0.5 "Who's Online" for Photopost Pro (v4.86) pages:
http://www.photopost.com/members/for...22#post1087422
The other methods posted in this thread proved fruitless, perhaps because I run Photopost Pro with it's "Friendly URL" feature enabled, which involves moving data that's typically passed in a URL query string into a format such as /photos/showgallery.php/cat/501 (rather than photos/showgallery.php?cat=501)
Hope this helps. The code changes are limited to vB3's functions_online.php file in the /includes/ folder. I preferred that over having to install an vB3 admin control panel hack, since this is pretty much a one-time fix for me.