The ajax search feature might look cool, but it doesn't always seem to work so good. There have been times when I've tried to add someone and it just couldn't seem to find them by username. (happens to be a multi-site with several hundred users) I was able to pull them up using other strings, but it seems silly that it goes through so many other names first.
The other part is that when I'm trying give all of the dev team access to the dashboard, it ends up being time consuming letting the ajax search feature do it's thing... admin, after admin, after admin.
Maybe it's just me, but I think it'd be SO much faster and more efficient to have the system automatically pull up the Admins and/or SuperAdmins. If we were able to simply check off each person's account in 1 step, then save as the next step, ... LOL... I swear, I'd at least have about 4 hours of my life back
The other part is that on some of these massive sites with a wide spread collaboration team, you don't even always know who's who with usernames. You 'should' know who's who enough to trust people as Admins in the backend, but I spend a lot more time in the WPMU DEV settings/dashboard than I ever do on the Users page.
...and now back to your 5 o'clock news