animating vertex group weight values?

blender 2.5

I’m looking at a simple cloth sim. I understand how to make a vertex group on a simple mesh that gets a weight of 1.00, for example. This group gets called in the cloth sim panel as the location of pinning, so that part of the cloth remains fixed in position. Is it possible to add keyframes to the weight of the vertex group, such that one can vary the weight over time, therefore affecting the weight of the pinning? Imagine a cloth slowly peeling off a table, or paper on a wall.

I see one can right click on the weight slider in edit mode on the mesh and get a menu for:

insert keyframe
add driver
add to keying set

and so forth. The insert keyframe command appears to add nothing in the graph editor window. However, I can add keyframes to the pinning command in the cloth sim panel, yet they appear to do nothing other than offer the option of being at either 0 or 1, unpinned or pinned. Yet when I change the values of the pinning keyframes, only the keyframe at the beginning of the animation has an effect. The subsequent keyframes are ignored.

I must be missing something very obvious. What would be ideal is if I could vary the weight value of the vertex group of any given mesh over time in the graph editor window; it seems there must be a way to do this.

ADDED: I see I can make keyframes for the stiffness attribute in cloth sim, and this has the effect I want if the vertex group controlling pinning has carefully selected weight, say .5. However, I would love to know if one can animate or change the group controlling pinning over time. Also, I’m stuck on how to keep a 2D mesh from showing a UV texture on both sides of the mesh. Unchecking the double sided option in the mesh panel doesn’t seem to do anything much.

thanks all
Faraday Cage