Hi guys,
Sorry if this is not the right place where to post the question: please, moderators, feel free to move the thread wherever it is appropriate

The questions are about meta-tags, and NOT only related to SEO
I'm a bit confusing about these questions:

1. What meta are really useful? Ok, "description" is Google friendly and we can spend weeks talking about how much "keywords" meta is useful or not... but, apart these, there are some meta like:
<meta name="MSSmartTagsPreventParsing" content="true">
<meta http-equiv="imagetoolbar" content="no">
that I find useful to hide that irritating bar on images in IE6, or
<meta name="pragma" content="no-cache">
to prevent page caching in some cases... Do you use them?
More, there are some meta which meaning or usefulness is obscure to me: I'm talking about URL, language, author, copyright, revisit-after, reply-to, document-rating, document-distribution, document-state
Is there an online guide that explains what they stands for, so I can decide what suits my needs and what I can safely discard?

2. Why there's a meta tag "title" if there is a <title> tag? Is there any difference? What is more important for SEO, among them? Can I fill them with same content? Can I discard the meta and retain only the HTML tag?

Thanks in advance for the answers