Whenever you’re deploying Windows Server DFS-Namespaces, you will need to figure out how many servers will be required.
Although we never really had any problems with performance of the namespace server themselves, the question of where to place them is quite common.

A single namespace server can typically handle thousands of referrals per second (the exact number will depend on details like the number of targets per link, the server configuration, the network bandwidth).
Since DFS-N clients will cache those referrals, you will be hard-pressed to find a scenario where a single dedicated namespace server would become a significant performance bottleneck.
However, there’s a lot more to this than raw referral performance, like fault tolerance or site awareness.

So, how many namespace servers do you really need? Jose Barreto has a new blog post to help answer that question at
http://blogs.technet.com/josebda/archive/2009/06/26/how-many-dfs-n-namespaces-servers-do-you-need.aspx