2by4 - 10:04 pm on Apr 12, 2006 (gmt 0)

grant, no need to think about it in complex ways, just look at a simple case:

site a ranks for green widgets, number 3

This term is searched for 1 million times a day.

If a large percentage of searchers return to the search page and click on the next option, it's quite clear that site a is not what the searchers wanted. Individual behavior isn't that important, but it's clearly one way you can measure how close the serps are to user expectations, that's why google included this in their recent patent application.

It's not the only way, of course, but it is one tool you have. And if I read the msn search javascript correctly, they are tracking clicks, although that script is hard to read, google's is radically simpler. About 1 line versus 50 or so... typical Microsoft.