Great answer, anothernoob. I agree, good caching makes all the different even the local squid and dnsproxy we setup locally made all the difference for our group of users.
I know what you mean about NTL caches birmingham has its fair share of up's and downs, it isnt running too badly atm. I remember when someone

from irc let me try out some un-used netapps and the browsing was lightning.
As far as the netnanny type apps that AOL give, they are ok but not perfect. They are basically a big block listing program with wildcards to deny access to certain sites. Things like dans guardian are intelligent content filtering proxies based on complex configs that have the potential to filter and block much much more in comparison to the block list files of netnanny.
I thought about the extra load it places on the caches and it probably isnt wise to place this on current proxies, especially the inktomi's. Im sure the degrade in proxy browsing is mainly hardware orientate so dual layer proxies wouldnt work either. Maybe a group of 4 or 5 dedicated content filtering NetApps seperate from regional proxies would do the trick. I dont think you'll get total smooth browsing with content filtering proxies because of checks on each object but thats the sacrafice you make to keep your kids safe. The only thing software wise that NTL could do is to develop a silent service to run on Windows (on our kids pc's) that forces the use of content filtering proxies.
Just a thought!