This is really powerful. Think about it...
Say you've read a tres cool thread on a modifying a sink base for the Soapbox Derby, and you want to save it for later use. Click on Edit Folders and name a new one: Modifications. There you go! Don't forget to save it.
Pay close attention. Although it looks like you are back where you started, you're not, Dorothy. Check your location by looking at the Subscribed Threads in Folder: "x". This time it's Modifications. Hit back to go back to where you were, or use the Jump to Folder feature above to navigate to a different folder.
But for now, click on your browser's Back button.
Now, below where you see Subscribed Threads in Folder: All (or whatever folder you're in), you'll see a checkbox to the far right of the thread title on the Sinkbox Derby - click it! See that dropdown menu next to the red Selected Threads: ? Drop it down and you'll see all your options. If you click on Move to Folder, you'll get another screen with another dropdown which gives you your choices of folders. Great! You can also do this with multiple selections, such as when you want to mass delete threads.
All in all, a pretty neat feature and one I intend to make use of myself.