>>> The ones which sometimes beat it are some 'orange' ones which redirect bad URL lookups to advertising-infested pages instead of returning 404s as they should.
That reminds me.... and whilst kinda on topic thought id mention it.
A few weeks ago I was having problems accessing a couple of sites that I knew should be working - such as Thomson Speedtouch and I kept getting the opendns advertising page thingy.
I thought Id removed opendns in favour of DNS Advantage a while back, but obviously not!
Anyhow I just couldnt seem to access the site and OpenDNS kept pulling up their ad page.
I removed OpenDNS and took the opportunity to add Bes new DNS.. and immediately I was able to access the site.