Here is what I have done to get unstuck...
I carry one of the snowbungie rope ratchets in my kit along with the full size sled bungie and a couple of webbing slings with some extra carabiners. Basically I put the sling around a tree, attach the rope winch, run it to the sled bungie (hooked to the sled) and put as much tension on it as I can. I should note that prior to this, I have dug the sled out a bit, stomped out the approach some and shifted the track over to packed down snow (normal prep). Once this is set up, I start the sled and pop the throttle while standing to one side and it pops right out and can be ridden away.
Disclaimer, of course this doesn't work if you have nothing to anchor to...