I have 8 web / app servers mounting multiple OCFS2 filesystems. The common stuff, Apache configs, logs, vhosts, etc and app code are stored there. I wasn't around for the initial implementation, so I can't speak much to that, but from what I remember off the top of my head, it's pretty standard with some modifications.
As for gotchas, it can be somewhat fragile. By this I mean, we had many instances where when a server left and rejoined the cluster, the load on all the servers would shoot through the roof for a few minutes. I think this was a bug though, IIRC after some updates the behavior is resolved.
The cluster configuration file must be maintained in the same state on each node, which can be a pain.
For us, updates are going to be a problem. We are on 1.4 I think, and an update to 1.6 means downtime for the entire cluster since the versions aren't compatible. You can't mix the two versions. Maybe on a anew deployment this isn't such a big deal.
Also, keep in mind a cluster fs is going to incur more overhead than a conventional fs. The more nodes you add, the larger the problem. The solution is more hardware (and good tuning).