The server environment is JVM-based since they expose GWT as the way to build UI. I think I remember seeing Rhino-specific error messages.

The coding environment is not very good, but you can build ERPs, CRMs, document management and similar for small businesses on Google Docs, in a way Microsoft Office / VBA never made possible. The modules it provides (spreadsheets, forms, formatted text document, gmail, calendar, wiki) seem to be very useful building blocks for describing your business processes.