Unfortunately, there's no customisation in Mbuntu, the application submenus are fixed. Also, while the "desktop" has icons for Messaging, Calls, Bluetooth, Contacts and the Ovi Store, no other icons to be added. Furthermore, there is no way to add icons or shortcuts for any other applications you have installed yourself.
Overall, this is just a novelty application for Ubuntu fans (which is probably why I am covering this story!). There's no real utility or advantage to using this rather than Symbian's own user interface.
Mbuntu is available in the Ovi Store for £3.00, which is expensive for what it is. Also, at the time of writing, Mbuntu isn't correctly showing for all compatible phones. For instance, it is not showing for the C7-00 when it is in fact compatible with all Symbian^3 phones.
David Gilson for All About Symbian, 7th February 2011