As far as I know, for business using google apps, if you have 10k employees you don't need to have 10k contacts, I think there is some kind of ldap integration.

Edit: See http://www.google.com/support/a/bin/answer.py?hl=en&answ... I don't think user profiles (that would be what is used for employees inside an organization) and shared contacts have a 10k limitation, only the user personal contacts have it.