yeah. i know i know, i havent been writing anything in ages but wth people, i too have a life (yeah right O.o).
however, some guy on the ableton forums gave me an idea for my old pre-live8 hack to get submix folder tracks. anyways, now we can group tracks and everybody is way happy about that, except a couple of users who realised that grouping tracks within tracks is just what we need. atleast this is what the feature request forums says.
well. the submix track hack still works, but now you can group it within a group. why would you want to do that?
as always the most logical reason is "why not?", but you can for example make a bunch of effect groups (banks or whathaveyou) with dummy clips with, say, a bunch of follow actions, then just place all those groups inside a group, and you can launch all of them via the grouplaunch button aswell as minimize the whole into one track only..
ofcourse you can do that while just grouping all tracks up to one group, but then you loose the organisation benefits + you loose the routing benefits.
the routing benefits? yeah, the routing benefits.
see, this way you can send audio to any chain in the rack, as opposed to the standard way of only sending to the track, which inturn sends the audio it recieves through all the chains. hardly optimal, is it?
this picture explains it all really.

as you can see, you cant route audio through a selected chain of your choice, however you can route midi like that
(or in the picture, audio via a custom plugin that just works as an audio throughputter;))
yes yes yes, i know you can do this with an audio rack and a chain ruler, but the difference is that with the chain ruler you can only have the output of the chains that are currently in the selected zone; this outputs everything as separate channels that you can route either to the group master out, or to other separate channels or whatever you want. it gets put to good use for organisational purposes but you can get very creative with it, so play around with it for a while ;)
since i recently switched to osx i played with screenflow, so heres a very cute little video of how to set it up, aswell as what you
can do with it as an example. the links to the plugins etc is at the youtube page.