Looks like Mavericks 10.9 has changed the behavior for adding application/document shortcuts to the Finder toolbar.

Where before you could simply drag any icon up to the Finder toolbar and hold it there for a second to add it, you now need to first hold down Option+Command and then start dragging the desired icon to the toolbar.

You can still remove the icons the same way as before: holding down Command, dragging the icon away from the toolbar and then releasing.

Source: Mac OSX Hints