So, it would seem the "secret menu" isn't some clandestine (but probably laminated) sheet underneath the table, but just an overall readiness to make custom orders.
The menu itself is just fan-made creations that don't suck. Which... almost makes it better?
Overall, the general consensus of the digital baristas implies that though making these items is generally annoying (as it's more work), the real annoyance occurs when you simply assume that every Starbucks employee in the world has access to this uniform "secret menu," which is obviously not the case.
This user, aptly named "what-size" sums it up succinctly.