I just had to share what I just discovered aftering seeing this post.
I thought I was going to have to buy the new, large, very expensive Cricut Expression so I could cut my chipobard. The Expression has a feature where the machine will automatically cut your image twice, which is supposed to work on chipboard.
Well, after reading and following instructions at the link above I successfully cut out chipboard letters with mine!!
Thought some of you may want to give it a try also!
Disclaimer: Keep in mind my chipboard is pretty thin (we use it for the back of pads and work) and this is probably NOT recommended by ProvoCraft. If you damage your machine trying this I will not be responsible. :)