I really had a difficult time to follow every single detail of the derivationon the 3rd page of the Shi and Malik paper, but i really liked the idea of normalized cuts.
As the authors emphasize this is in the paper one of the best property of this measure is that minimizing this messure naturally leads to the maximization of the normalized association within sub-groups.
The results presented were promissing, but were not intuitive why the segmentation algorithm selected certain parts (od the zebra) and neglected others which were clearly different from their environment.