Using Adwords free tracking tool to measure keyword relevence:
Google Rolls Out Keyword Conversion Tool:
"Mobile-device software seller Iambic, one of the first AdWords' advertisers to use the conversion-tracking tool, said it would allow the company to better allocate its $1,500 per month AdWords budget.
'We couldn't figure it out,' said Iambic's director of marketing, Sebastian Dijmarescu, of the return from AdWords' campaigns. 'It was a guessing game.' " conversion tracking allowed him to see clearly which keywords were working best. Google's campaign management reports carry a keyword campaign's conversion rate and cost per conversion.
... The new conversion-tracking tool is free to advertisers, allowing them to insert a line of JavaScript into their Web pages to track whether users arriving via keywords convert. In addition to purchase conversion, advertisers can track if a user signs up for a newsletter, views certain pages, or qualifies as a sales lead by giving contact information. As an additional benefit, advertisers can have the value of each conversion sent back to Google and included in their reports. "

API tool to monitor results for search terms & any changes in SERPS - :
20 Great Google Secrets: "Google Alert (www.googlealert.com) monitors your search terms and e-mails you information about new additions to Google's Web index. (Google Alert is not affiliated with Google; it uses Google's Web services API to perform its searches.)"

How google spiders prioritise sites to crawl:
CanadaIT.com - News On The Web: "Nevill-Maning showed a pyramid diagram to illustrate how Google organizes its searches. At the bottom is 'main,' where there tends to be higher latency for pages that don't change very much. 'Fresh,' in the middle, includes portals that need more up-to-the-minute checks, like e-commerce sites during the December holiday shopping season. On top is 'News,' for CNN.com and other sites that change all the time.
To maintain the relevancy of its search results, Google hires PhDs with expertise in machine learning to create algorithms that look for links to other sites -- what Nevill-Manning called the company's secret sauce. "

"a company rule stipulates that 20 per cent of their work hours can be devoted to brainstorming. "We don't quite know what it will be useful for," he said of Google Sets, "but it's awfully fun."