Quoting Eric F Crist <ecrist at secure-computing.net>:

>>
>> Yes, sudo logs all commands that are run through it.  su doesn't.
>
>
> This is slightly misguided.  Even with sudo, you can sudo su <user>
> and where the su to <user> will be logged, anything done while su'd is
> not logged.  Only commands invoked directly with sudo are logged.  In
> this case, logging is no better than it is with su.
>

Note that the proper approach here would be to simply disallow doing a  
sudo to su if you're on a multi-user system where such things matter.  
One of the nice things about sudo is that you can specify with a fair  
degree of granularity what users are allowed to issue what commands as  
the superuser.

Josh