I cannot eject anything from Finder, either by clicking the eject icon in the sidebar, or by dragging the icon to the trash (it does turn into an eject icon though). I'm using Disk Utility to get around this, but it's frustrating to have to open that up when I'm staring at Finder all day long.
This is a recent development, as it was working fine before. I haven't installed anything new that I can associate with when this started happening.
ETA: I managed to fix this myself. Trashing the Finder and sidebar preferences and then restarting Finder did the trick.
Best Answer
If this behavior persists past a reboot, you might need to go down some general problem isolation steps:
There used to be an article (it's gone or I can't find it at the moment) that walked you through setting aside the application preferences or testing this behavior in a new user. In your case - it looks like you figured it out, but I wanted to at least mention the official guide in case others have the same symptoms but a different cause.