Have you spotted folks with the last name Resident yet since the change? I've seen a few. Lots of Noobies have been coming to Lesbos lately. According to Tateru Nino on her blog (Web), new registrants are automatically assigned that last name. No more scrolling through lists or hitting refresh again and again until you see a last name you like. On a similar note, if you see avies named something like 39873 Guest, then you've found someone trying the Web portal Beta (Web). I gave it a whirl today and it worked very well. I'll have to try it on my iPad soon.
With Display Names, though, I learned that if you set a name and don't like it you are not stuck with it for two weeks, as the various Second Life official Web sites indicate, but if you hit the Reset button on the name change pop-up your User Name is restored as the name everyone sees right away.
Addendum: I've seen some prize givers of late that use initials of last names as well as first names (the latter style invented by Shep Korvin of Lucky Designs). I wonder how the standard last name change is going affect those. Or how names will now appear on Contest Boards at events. I might have to make an alt to find out.