ns_cache needs to be vserver-aware if virtual hosting of multiple OpenACS 4 sites is going to work. But given that AOLserver 3 didn't have a built-in virtual hosting solution at all this is no reason to avoid using AOLserver 4.
But we should remember this. I've just downloaded the porting guide but don't know when I'll find time to look at what it would take to get ns_cache to maintain a separate global cache for each vserver.
