Whoa, what's this "Show All" button doing in the toolbar? I still think a Home icon makes the most sense; "Show All" could mean show all mouse options, etc, whereas I think home is clearer that it'll go to the home screen. Just my thoughts.
Just tossing in my two cents; unless I'm much mistaken, you'll only be able to reach specific plug panels via the main Switchboard window, yes? If this is the case, then "Show All" makes sense in that, you were just viewing a list of all plugs, and would like to go back to the view.
If this isn't the case, perhaps "Show All Plugs" would be evident enough? I'm in general agreement that a home icon feels out of place here.
Generally I love it. Though I think that the the switches and their labels waste a lot of space - especially in the multitouch pane, where it's not overtly clear that the switch is placed so far right so as to line up with the "Natural" switch in the pane above. I've gone ahead and done a quick re-arrangement of the panel that I think makes better use of whitespace, and makes the alignment a little more clear - and I'm about 95% sure it follows the elementary HIG
You would only want to disable a certain multitouch gesture if you could make it do something else. Since you can't do that (or am I missing something?) it doesn't make much sense to allow disabling these gestures. It would make sense to get rid of all those multitouch checkboxes and add a (?) (like your About dialog mockup) to show the list of gestures in a support article.