> Install NetBSD 4.0_RC3 onto a machine which does NAT for a modest sized 
> network. ipnat -l | wc will show a constantly growing list of connections. 
> Networks which would normally only average around 1,000 connections show 
> more than 25,000 connections in a day or two. Networks which average 
> around 50 connections show more than 20,000 after four or five days.

Probably caused by http://releng.netbsd.org/cgi-bin/req-4.cgi?show=880
which will be backed out soon.