We manage 2000 sites on our WPMU installation.
When logged in as a super admin user, the admin area takes up to 15 seconds to load between pages. When logged in as a single site user, it's 2 seconds between pages (joy).
Therefore, we suspect it's the 2000 sites loading in the header utility bar that's slowing things down.
Any options to speed things up when logged in as a super admin user?