WIth current glibc's (tested on RHL62 and RHL71), it's pretty safe to
remove
'--with-ipv4-default' from openssh compile-time options.

This makes it so that when you connect like 'ssh some.box' ssh will first
do a AAAA
(IPv6) DNS lookup, and after that fails (~0.1 sec or less), does the normal
A query.

Some other vendors have also been enabling this, e.g. Mandrake apparently.

In practise, all this means is you don't have to use 'scp -6' or 'ssh -6'
when connecting
to ipv6 hosts.

Only apparent side-effect I have noticed (apart from AAAA query), on a box
where there is no IPv6 is:

Jun 26 10:45:23 pajulintu modprobe: modprobe: Can't locate module net-pf-10

when sshd is started.   This is good because if there would be 'alias
net-pf-10 ipv6' 
in /etc/modules.conf, sshd would autoload it which wouldn't be the intent
(the alias is added by initscripts if NETWORKING_IPV6 is set)