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.