A web page could be encoded in nothing but div and span tags. However, search engines do not process those types of pages very well. They like material to be marked with tags that identify the type of material e.g. Headlines, Paragraphs …
From a page design standpoint a time tag is the same as a span tag. But looking outside of the page itself it provides information to the outside world about that particular piece of data, page or article.
The simplest format is <time datetime=”2009-10-22″ pubdate>October 22, 2009</time> or <time datetime=”2009-10-22″ ></time>. An RSS type of format may also be used <time datetime=”2009-10-22T13:59:47-04:00″ pubdate> October 22, 2009 1:59pm EDT </time>
This information is very useful to researchers and greatly expands how search engines can offer up search results. Timeline searches are not exactly mainstream right now but that does not mean they should be ignored.
Google explains how they use microdata for their search listings here Microdata support for Rich Snippets
Now some may not see how they could use a review of a product they sell posted on Google to their benefit. I’m not worried about that – I’ll be glad to let people see the stars on a listing and if they need more information or want to buy the product – well they need to click on the link, it’s available 24/7, and I’ll be glad to sell the product.
I see designer after designer that charges for sites by the page; who also create logos, postcards … (brochures, fliers, etc) … Looking at their designs obvious SEO keywords are done in graphics or embedded into flash (and still as a graphic). Sometimes they include keywords … SEO, web 2.0, PHP, HTML … at the bottom of the page in un-formatted text, (even labeled as keywords), in a structure that is not grammatically correct for their ads. I guess the semantic web isn’t the only thing being ignored, I don’t think those keywords are intended to WOW the people who look at the ad.
I guess it could be worse they could have specials like … “8 page web 2.0 site only $299” …