Not managing keys is asking for trouble. Consider signing your SSH keys to validate that you've properly pruned outdated host entries.

See:

http://www.openbsd.org/papers/asiabsdcon2011_openssh_whats_n...

http://blog.habets.pp.se/2011/07/OpenSSH-certificates

http://en.community.dell.com/techcenter/b/techcenter/archive...

Spend an afternooon to figure this out.