Which ones matter or are they the same thing. Most important keywords should be in big letters right? Or in H1? If they are the same thing, what is font size then? If they are different, isn't using H1, H2 just s p a m because same looking sites should behave in the same way.
I don't think Google reacts to font-size. However in a proper article for example a <h1> would represent the title or header, and the <h2> would represent the sub-title.
Yes. A common Black Hat technique is to make H1/H2/H3 the same font size as normal body text. The Black Hat then puts the terms he wants to optimize for into H1/H2/H3. Everything looks normal to visitors, but the search engines see the H1/H2/H3 terms as "more important on this page." This technique may or may not function on any particular search engine at this time.
I always change my size because i dont like huge font and never had a problem. But like Will said just dont make them the same size as everything else and hide it.
I normally use H1 for my site keyword, and H2 for sections related to the keyword: e.g H1 - for Men Underwear H2 - Tight Underwear, Loose Underwear, Sexy Underwear and use external css to make sure H1 and H2 doesn't look enormous & ugly.For example: h1{ font: bold 120% Arial,sans-serif; color: #334d55; margin: 0px; padding: 0px; } h2{ font: bold 114% Arial,sans-serif; color: #006699; margin: 0px; padding: 0px; } (.. no guys, I don''t sell underwears. So don't pm me to buy any underwears )