I will never do this, and have no idea how it could even be done, but maybe some programmer can pick this up and go with it, it would be perfect link bait for a site. My idea: ok you know the silly little green PR toolbar? How about a silly little SEO hat? You would go to a website, and depending on the on page factors and backlinks to that site the "SEO hat" icon would change color from white, different shades of grey, to black. You'd get an instant snapshot of how that sites seo practices are seen by Google. Or how your sites are seen. You would know who is safe to link to and who to get links from hmmm...i bet a smart programmer could make it happen
If it looked for black hat techniques and could identify bad websites linking in, then it would be awesome.