I am currently active on 4 Stack sites, and to switch I click on the "StackExchange" button, click on "all Sites", scroll until the site I look for appears, mostly at the bottom of the list, and then click the site. Very annoying.
Since you alreay know the accounts one is connected with, why don't you let us choose which we want to have linked on the start page? I would love an small 16px icon for each site I use regulary at the right of the "StackExchange" dropdown. Maybe You could just add some checkboxes in the preferences page where one could select the sites one needs, so not all my sites appear, but just the 4 I would check.
This would make it more comfortable to have a quick look at the other sites and answer questions there... currently is switching just annoying, and so I just stay on StackOverflow.
PS: I know I could bookmark each site, but I often switch the clients I use, and don't want to have to create bookmarks on all these sites, when usually a quick "stacko" in googles search field is enough to get here.