I just found out about the Web2DNA Art Project, which will analyse any website and create an image of it’s ‘DNA’:

The brightness of the lines is determined by the importance of the tags in terms of structure.

H1 is brighter than H2, which is brighter than H3.
TABLE is brighter than TR, which is brighter than TD tags.
Images and flash elements appear as 70% white.
New HTML tags like STRONG and EM is brighter than older ones like B and I
UL, OL and DL is brighter than their LI, DT, DD
DIV layout is brighter than table layout

Basically a semantically rich site will appear brighter than one with messy old-style code.

The image above is of this site, but you can try it with any URL. For some reason though, it doesn’t work in Firefox…

Thanks to Martin for the link…