Stan Barber's Notes RFC 1631 outlines what a NAT is. In this presentation, Cisco technology is used. This has worked with 70 concurrent incoming transtions, many applications and many rules. Kerberos V4 will never work SNMP will never work Mobile IP will probably never work.
More stuff needs to be tested.
There is a real desire to try to get this to work with multiple ISPs. We basically leave it to the customer. We don't do a lot with overloading. All the connections to the NATed hosts are available when just one of the NSP connections is up. This does not break that.