InfoQ has an interesting article about Adobe's Collaboration Platforms including ConnectNow and AFCS. In it Raffaele Sena who is a Senior Computer Scientist in Adobe's Business Productivity Unit talks about the scalability challenges of a system such as Connect and how the team has addressed them.
In particular he mentions the use of Terracotta and how it helped scale the system by providing the cluster with distributed memory that also makes failover scenarios much easier to handle. It's an interesting read.