Yeh, FYI is cool, and thanks for the tip on buttonsnap re low bandwidth users although I've had no problems as yet. I've even tested on a 300mhz Pentium 2 and 56k modem connect which was way slow loading the whole javascript heavy WP admin but everything was functional.
The 'make people install' thing is more for the WordPress sites I maintain but also WPMu admins like myself, I'm running 4 Mu's at the moment and prefer the plugin path for customisation rather than keeping track of custom Mu's through the constant Mu updates I've been running over the last year. Drag and drop into mu-plugins folder on a vanilla Mu, activate and forget.
Still, some tinyMCE plugins could be good for Mu so long as it doesn't involve custom tinyMCE configs. Last time I looked you could invoke them from an mce_buttons call in the plugin, same as I do with buttonsnap at the moment. Might put it on my todo list which as usual is never ending. How do you call yours up into the rich editor?