Running namecache service on postfix server?

[Robert Moskowitz]

I have recently updated my DNS server and am observing the traffic from 
my mail server to constantly query for names.  Some of these names are 
frequent requests, for example: zen.spamhaus.org.  So I was thinking 
that I could benefit from running a namecaching setup on my mail server 
platform.  This would cut down on traffic and time on my mail server.

Is this a practice that is common?  Are there any downsizes to doing this?