Since it took me an embarrassingly long time to figure out why “use kerberos keytab” refused to work in Ubuntu 9.10, I’m posting here what my problem was.

It seems “use kerberos keytab” is deprecated (as noted in the release notes). The replacement is some variation of kerberos method =
If using the system keytab, that makes the option simply:
kerberos method = system keytab