Found a nice tutorial on Stretchy Bones in Maya. At first it's a little scary to understand but it's basically talking about the use of the "Measure Tools" which yous pecify in using the "distance" tool, which basicaly shows you how far you distort the measured object, as well as including the use of expressions. The expressions are a little tricky to get your head around but it's laid out as simply as it can be.
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Also the final product is available to download at the bottom of the tutorial. You can access the expressions used within the file also which is a nice finishing touch to the tutorial. :) I'm going to have a gander a little more with this probably tomorrow.