Apple has moved Directory Utility from /Applications/Utilities/ to /System/Library/CoreServices/ .
It can also be accessed through the Accounts System Preference by going to Login Options and clicking "Edit" next to the network account server at the bottom. There is an "Open Directory Utility…" button there.
It also appears that Firmware updates have a new location in a folder in CoreServices, which is rather nice.
Next up, it looks as though the Kerberos application has been renamed "Ticket Viewer".
The 10.5 only application "Directory" seems to be missing in action. I was hoping that its functionality was merged into Address Book, but it does not appear to be the case.
Please add any others in the comments below.
by 
Don’t forget you can always …
open -a Directory Utility.app
peet
Directory has been replaced by iCal Utility that is part of the Server Admin Tools
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ACSA, ACT, and other assorted acronyms of varying and asundry import.
MacTEK Consulting & Training, Las Vegas, NV
In part.
It appears you can add locations and resources with the iCal Server Utility. However, you cannot modify groups the way you could with Directory. It was a great app for delegate admins (think department heads) to be able to take control of their group permissions. Now to do the same thing, they have to have Workgroup Manager and Server Admin, which I don’t really want anyone other than IT using.
Also it seems there’s no replacement GUI to modify “People”, that is contacts that are not Users.
Still you can create them via WGM, using inspector and adding People records with the attributes you need. These records will be accesible via an LDAP or CardDAV search using Address Book. For CardDAV access the directory gateway option in Address Book’s service in Server Admin must be turned on.
I think that is implemented in Address Book, as Address Book Server is where “People” should reside, rather than in the actual directory.
Ticket Viewer seems to be much less useful when compared to the old Kerberos.app. It seems you can change/add/remove identities, renew your TGT, and change your password, but you lost the ability to see individual service tickets, or get any info on the details of your tickets. Also, the old preferences are gone. There is nothing to configure.
The good news is the old App seems to work fine on SL, and if you don’t mind getting under the hood, or creating your own tools, the CLI tools are still there for mucking about or wrapping. I still don’t understand why this move was made, unless Apple had some sort of falling out with MIT (the old tool was MIT’s, not Apple’s).