I'm a pretty big fan of Likewise. I am currently using the likewise open version on many of my linux boxes so that I can authenticate against Active Directory. This makes my life easier in the fact that I don't have to deal with adding and removing users from these boxes.
Our standard build consists of a build that has sudo installed. Root cannot login over SSH and we have a default local account that the sysadmins know and can use if in a pinch. We do, however, use our own accounts so it can leave a sudo log trail.
Now, when we installed likewise-open on our default ubuntu image, we had one concern, any user with an Active Directory account can now login to our Ubuntu servers. While they will just be a dummy user with minimal privileges, what is to stop these users from using an exploit to escalate their privileges to root, or filling up their home directory and owning some of the boxes that don't keep those partitions separate. While I don't think any of my users would do anything like that, its always better to allow minimal privileges and lets face it, my sales, accounting, managers, and many others have absolutely no business in ever logging into any of the production linux/unix servers.
I did some strategic Googling query building and I was able to stumble on a thread (sorry I lost the original link) that pointed me to a specific line in a configuration file (/etc/security/pam_lwidentity.conf). By uncommenting this line and putting a group in there, I can restrict who can login to my servers. So I set it to the following and simply created a security group called 'unix admins' in Active Directory to hold the people who can admin these boxes. Piece of cake.
require_membership_of = GCA\unix^admins