Now in your Other Users nodelet you will see a chatterbox "topic" This is where the gods will post small announcements not worthy of news on the front page, or simply harass you. Because it's fun to watch you squirm. Anyhow.

But I never visit Other Users or I have it turned off

You are also given the option to move it down underneath the talk button in your user settings, home of everything that's right in the world. You can outright ignore it by shutting off whatever nodelet it's in, if it is such an eyesore for you.

The topic goes away when I change rooms!

Topics are by room, and thus it means that a god hasn't set the topic for the room that you are currently in. Unfortunately you can't set the topic just yet for room that you are in.

Will I ever be able to set the topic?

For the time being, no. Will you be able to in the future? No one ever knows; try a fortune cookie

I'm level 5, and really dig Create Room. I can't set the topic on a room I just created

Unfortunately, due to some implementation choices that were made way back when, you can't set topics on rooms you create just yet. Someday perhaps. Have another fortune cookie.

Comments and bugs should to go JayBonci