If it works anything like Websense here is a tidbit of info:
We were having problems with our manufacturer websites getting filited and categorized as something other than automotive (something similar, I forget the category). It was getting cat as "shopping", "sports&entertainment", and a few different things which we have blocked.
So we called up websense to bitch. It turns out that they dont actually filter then URL such as
mybusiness.com,
Up At Six HTTP Server Test Page, etc. The filter by IP hosting said site. Researching a bit further we come to find out that large companies will have mutiple servers hosting their websites, so pinging a url such as
Lexus: New Luxury Cars and SUVs from Lexus USA might actually resolve to several different IPs. The problem with this is that on those same servers (IPs) they also host other websites from companies large and small. So say if you hit an IP that is hosting Entertainment Weekly's website along with Lexus website, it will get categorized as "entertainment" across the board for all the sites, regardless if they are actually entertainment or not.
We have SonicWalls in our network, but I am not sure if they operate the same way Websense does.