The last one. Per default it is using API V.1 (except from the parts already using V.1.1, of course, like the tweeter and announcer). For any generic user independent functionality (like searches and tweetbacks) you can switch to API 1.1 in the configuration of the sidebar plugin and the tweetback part, but have to choose one of the OAuth'ed accounts of the main configuration then.
The configuration is easy, but have to be done manually (as I don't want to use an OAuth acc here w/o asking).
It's a cool idea to have a message for that in the admin startpage. I didn't know, that I can do that! I will try that and do an update for that sooner or later.
P.S.: For admins understanding German I put a hint about what to configure in a blog post.
Creating and modifying plugins.