(I also posted this on scalug)
A friend of mine has an interesting situation. Their DNS server gets 
around 2 to 3 million dns queries a day its running on a quad xeon 
system with 4 gigs of ram. Its running Bind 9.2.2.
At least twice a week if not more their server will stop looking up 
domains that are not cached.
They end up having to restart bind to get things working again.

Any ideas?

--Adam