> On my systect it takes very short time:
> rochebonne:~> /usr/bin/time su
> Password:
> rochebonne#/home/bouyer>exit
>         1.87 real         0.01 user         0.02 sys
> 
> (most of the time is used to type the passwd :)
> 
> 'su -' is a bit slower (1 more second on my system) because it starts a login
> shell. The shell has more work do to and source more files (e.g. su to a user
> with a [t]csh shell will source only .cshrc; while su - will also source
> .login).
> root's .login will call 'tset -Q' which takes some time (without this, on my
> system su and su - uses the same time). Did you check root's .login ?
> 

For both my alpha and i386 systems, I rebuilt login without kerberos
support and saw imporvement.  I noticed because I have a krb5.conf file
that is use when I'm at work, but only need it for client programs.

Both times I edited /usr/share/mk/bsd.own.mk, but perhaps there is a better way?   
/etc/mk.conf NOKERBEROS?