If you're in native mode, and don't have Win9x or NT machines lingering around, then it really depends on whether you need it.
In a single location, you don't need it. You might need it you're using Exchange in a complex, multiple location environment.
If you DO have 9x & NT boxes, then, yes, you need WINS.
Pat Richard, MCSE(2) MCSA:Messaging, CNA(2)