At my day job I'm a search engine optimisation wallah. Google does return different results to different computers based on a number of things. If you're signed into a Google account you will sometimes see different results than when signed out. There is also a geographical variation and occasionally inconsistencies depending on which data-centre handles your query. As for the search ranking algorithm, Google's algo is still based on the PageRank model, where the number of links into a site is seen as an indicator of quality, but there are more than 100 elements in addition to that, and Google, not surprisingly, does not publish details as they think people like me will exploit the information. Other things that influence the ranking of websites in G search results: age of website/domain, quality of inbound links, relevance of inbound links, presence of keywords in domain name, age of inbound links and the pages that bear them... On page stuff does, as you say, include HTML titles (the most important on-page element), heading tags etc. Ranking factors don't have any bearing on the variation you see between computers though.
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