There are some warnings (not exactly problems, you'll see it) you must when developing your app.
Store session on memory + Cluster mode enabled
The cluster mode runs a new instance of your app for each core of your processor, so they won't share objects between them. When using sessions stored in the memory (e.g. in an object, using MemoryStore), that object won't be shared between the instances of your app, so the user may lose its session data.
To understand it better, read how Cluster works, in Node.js documentation.
Cluster mode enabled + Superagent (or compliants)
If you're going to run tests that use the Express instance inside your app (e.g. Superagent), you got to disable the cluster mode. It happens because this instance will link to the master process when the cluster mode is on, that do not have routes, and it'll fail.
Fortunately RhapsodyJS allows you to enable Cluster just in some environments, so you can disable it in tests!