I can't believe this just now happened to me, but for the first time since I started using AutoCAD 2007, I needed to cycle through some overlapping entities. I used to use Ctrl+Click to cycle through entities stacked on top of each other. Since the 2007 version of AutoCAD Ctrl+click is used for sub-object selection on 3D objects (face, edge, vertex). To cycle through stacked entities, use Shift+spacebar or Ctrl+spacebar.
If you enjoy living in the past, set the LEGACYCTRLPICK system variable to 1 to return cycling to it's classic behavior.