[mariarmestre]

I think a fundamental issue with search, and the reason why many companies do not invest in tuning a good search experience, is that the main metric usually is to minimise embarrassing/irrelevant results, rather than get the best possible set of results. How can you even know what is the best answer to your query? Systematic evaluation is very hard.

[TimPC]

If you control the browser your results are in you can monitor clicks and time spent on document to generate pretty good signal. If someone opens a document and looks at it for fifteen minutes you should be fairly convinced it was useful.