Welcome to the Q&A Forum

Latent Semantic Indexing http://www.seobook.com/archives/000657.shtml I think they definitely do that for spamming reasons, otherwise you could make a million pages with latin text and only put your keyword repeated in the content and get it ranked. A real article speaking about a topic would generally have similar related words also included in the article.

How large is your site? Bing WMT offers a means to directly submit up to 10 links per day, up to 50 per month. I would recommend adding any category pages for your site which are not indexed. Next, go through your site and add any missing sub-category pages. Once these steps are done, you can begin adding your most important pages.

I'd suspect that if you change the date, and ping rss aggregators, they'll publish the content, which then becomes 99.9% duplicate content.

There's a fresh post on Search Engine People yesterday about blog commenting guidelines that likely mirrors what many people here would say about commenting. http://www.searchenginepeople.com/blog/blog-commenting-guideline.html It's a good read for developing a comment strategy that will work in the long term.

I agree with Ryan and EGOL. Spend your time and energy on making content that users want to read, not in trying to outguess the search engines.

I doubt this will dilute the effectiveness of the keyword - what I would be more concerned about is a potential ranking penalty. I have seen this technique used in the past but hardly ever see it being effective these days. I would stick to crafting well crafted titles designed for the user in mind - keeping your keywords first in the title.