Should DNS be on same server as webserver?

[John Almberg]

The other day, a FreeBSD 'expert' told me that it is important to  
have the DNS server for a domain on the same server as the domain's  
web server. Supposedly, this saves doing tons of DNS look ups over  
the network. Instead, they are done locally.

This makes sense to me, but I wonder if the performance difference is  
really that significant?

-- John