HOW DOES GOOGLE WORK
Google is the #1 search engine as measured by market share. Arguably, it owns 67% of the market - ahead of Yahoo, AOL, Bing, Looksmart family etc. Google also powers other search engines. Google also draws results from the DMOZ directory although it consistently places these results below its top choices from its own search algorithm as supplementary results.
Google is focused on speed and efficiency. In addition to crawling your title and body text, Google weights about one quarter of its search algorithm to establish a theme from the links that are pointing at your site. It is looking for quality links that share relevance to your site that point at you. It also crawls back into those links and tries to establish how strong your theme carries through or whether the site should be reduced in rank due to the use of purchased links. To do well on Google, you need links that share relevance with your site, pointing one way or virally through news and social media to your site. You can achieve this by registering with service directory sites that match your theme.
How many themed links do I need? Well it depends on site quality and volume of the links that are pointing at you but 10 strong links is ok - 300 is better – 1,000 is lots – 20,000 you're putting in more effort than necessary. Once you are listed on Google you should be aware that Google reorganizes its listings many times per year. Google has 10,000 Linux servers sharing data and during this sort which takes two or three days sites get added, sites get dropped, placement changes and new algorithm factors kick in. Some of the placement changes are temporary and some are permanent.
Basically all hell breaks loose and good web masters pay attention to the output of the re-indexing and make adjustments in preparation for the next go round. With millions of new sites indexed by Google every day it has a daunting task to organize all this information and present sites that best match a search query in the blink of an eye.