For those who don't know: Unity is the new Ubuntu Netbook Edition interface which will be available for Ubuntu 10.10 Maverick Meerkat.
This was something pretty much obvious, but now Mark Shuttleworth confirmed it: the Unity panel won't allow any kind of customizations. That means not only that you won't be able to add/edit applets like in Ubuntu Netbook Edition 10.04 (which could be easily "fixed"), but the user won't even be able to right click the applets to move them or whatever - nothing will happen upon right-clicking.
I noticed this ever since I first tested Unity but I had hoped some kind of customization would be allowed in the end but it seems that won't be the case. The reason for this is to "feel cleaner":
That's why we only support left-click on the indicators. When in gnome-panel, the right-click is used to manage panel features, but in Unity there's no such capability, so it will feel cleaner.
It seems the right click has been completely removed from Unity: right clicking the top panel, the new dock or the desktop - does nothing.