Just been playing with Mahara a bit. Writing plugins is not as traumatic as I had expected. I got a very simple Flickr Feed demo going in a matter of hours. I simply made a Mahara adaptation for a jQuery plugin written by Joel Sutherland. (it requrires Mahara 1.4 which hasn't been officially released yet).
A lot of very cool plugins have been contributed within the jQuery community and it wouldn't be very difficult to turn them into Mahara content blocks.
The question then is which ones would be useful to have on Mahara? Do students or teachers sometimes reques for new plugins to be added? If yes, which ones?