If you used custom motion paths in PowerPoint 2007, you may think a setting you previously used has disappeared in PowerPoint 2010. In PowerPoint 2007, to get to Curved Motion Paths, you would select from the Animation Pane Add Effect > Motion Paths > Draw Custom Path > Curve.
In PowerPoint 2010, the path is a bit different. To insert a custom motion path, click the Animations tab and then choose Add Animation > Motion Path > Custom Paths. You will notice, however, that the custom motion path options you once saw in PowerPoint 2007 are not there.
Never fear, the option isn't gone, it has just moved. After selecting Custom Path, return to the ribbon. Select Effect Options from the Animations tab to find the Custom Path options for Curve, Line and Scribble paths.
For more on motion paths, check out this article on Perfecting the Motion Path.