Recently VMware Technical Support Posted KB Article 1006803 which shows a supported method for clustering VirtualCenter Management Server 2.5 using Microsoft Clustering Service. It isn't the only way supported, and VMware Support will work with you if you are trying a clustering method that is a little different, but this is one documented method.
We have had a detailed document on how to cluster VCMS since VirtualCenter Management Server 2.0.1 Patch 2, and now we have a documented use case that works and is updated for VirtualCenter Management Server 2.5.
Now, you can have VirtualCenter up and running, and if something happens to the box, you can fail the cluster over to the other system running MSCS. If VCMS isn't clustered you don't lose anything if VCMS fails (except possibly tasks in progress), but now you have more redundancy and it comes back more quickly.
One of the nice things here about Clustering VCMS is that you can run it all inside of Virtual Machines. This means that you can have a backup copy of your VCMS server without having to buy any new physical servers to place it on (run it on your existing infrastructure)!
Now, I haven't played with it much, but I just got a lab with some servers and shared storage. I am getting excited about the opportunity to give this a try. With VMworld coming up, I may not get to it until after, but I will get to this and report back what happens.