This is the abstract of technical report TR-ARP-07-94 (dvi or ps)
Despite over 25 years of its use as as the standard example in planning, Blocks World (BW) is still little understood from a mathematical point of view. Here we report a series of investigations of this surprisingly complex structure, issuing in:
We close with an experimental comparison between our new algorithm and certain others suggested in the recent literature. All of these algorithms have the property of being `near-optimal' in the sense that for some constant k they guarantee plans no longer than k times the minimum possible.
For more on Blocks World, including an online problem generator, see the Blocks World Page.