David_Hill - 8:58 am on Nov 18, 2010 (gmt 0) [edited by: engine at 1:25 pm (utc) on Nov 18, 2010]
This will depend a lot on the spider. Many spiders completely strip all HTML from the document, remove stop words and then index the remaining words. Search engines use algorithms such as PageRank and topic PageRank to sort results.
To be quite honest with you, I would not spend any time modifying my HTML for SEO. Your position in a search engine really has more to do with content than anything else. And even though you did not ask, I would be highly suspicious of any company claiming that they can greatly improve your position in a search engine. Spend your time creating great content and the rest will take care of itself.
[edit reason] Promotion removed [/edit]
[edited by: engine at 1:25 pm (utc) on Nov 18, 2010]