http://www.davidegrayson.com/signing/
Discossion on private key re issue and others"
http://security.stackexchange.com/questions/27810/should-i-change-the-private-key-when-renewing-a-certificate
Check this link out for some publishers opinions:
http://successfulsoftware.net/2008/02/27/the-great-digital-certificate-ripoff/