Resolution:
Yes.  There are two misleading statements in the PortalBuilder documentation which could cause problems.  

Please disregard the two notes in the PortalBuilding Guide and the Content Publisher Guide that suggest to use %%serverurl%% in the Source URL of CP categories (Content Publisher catgeories).

CP categories are HTTP-based. As with all other HTTP-based categories (Parsed HTML, etc), you should avoid any "thread loopback" condition.  In other words, your source URL should not point to the same web server that hosts the PB instance that receives the end-users' request.

"Thread loopback" can cause resource deadlocks at the web server level under high load conditions.  This will make the server unresponsive and appear to be "frozen."  Once you get into this state, a web server restart is often the only way to correct the condition.

Are there any issues around the use of the substitution variable %%serverurl%% in ContentPublisher or HTTP-based categories?