3D Views and Animation
There are some important visualization features in the 3D views that can help animation.
When the current frame is a keyframe for the current active object, the name of this object (shown in the bottom left corner of the 3D views) turns yellow.
The 3D Views can display “ghosts” of animated objects (i.e. objects which have keyframes defined for some Object Ipo curves). These ghosts are outlines of that object, as it is at the corresponding keyed frames.
To disable/enable these ghosts, you can either hit K in a 3D view, or click on the Draw Key button of the Anim Settings panel (Object context and sub-context, F7, in a Buttons window).
By default, all keyframes of the object are shown. You can display only “selected” keyframes by enabling the Draw Key Sel button, in the same panel. This implies you can select keyframes, hence that you have an Ipo Curves window in Show Keys mode (see this page).
Note also that armature’s bones have much more advanced ghosts options, described in the rigging chapter.
Unfortunately, this display feature seems buggy, at least with some graphic cards you might have problems to see it (for example using 5730 ATI mobility chip, under Debian squeeze)