Since I started my feed project, I've been amazed that webmasters who wouldn't dream of not putting alt text on an image, do not tag their posts.
Here's an article that I think explains why you should be tagging your posts.
Think of tags as keywords for your specific post. Most the blogging scripts have a tag plug-in but you can do it with html if you prefer...and it's just like a link (example of a technorati tag).
HTML Code:
<a href="http://technorati.com/tag/babes" rel="tag">Babes</a>
So, if you've claimed your blog on technorati and you ping them, they will pick up the tags and your post will get added to their search engine.
Don't want the traffic leak to technorati but still want indexed? This tag will work equally as well.
HTML Code:
<a href="http://technorati.com/tag/Crimson+Ninja" rel="tag" />
I have optimized
XXX Blog Feeds for tags as well. So those participating could setup their tag
HTML Code:
<a href="http://www.xxxblogfeeds.com/tag/babes" rel="tag">Babes</a>
and still get the benifits of being indexed by technorati when they ping and give a site your feeds are being displayed at the benefit of the linkage.
Oh, and everything I've said goes for Del.icio.us and all the other social bookmarking sites as well. If someone bookmarks your site, the tags on the post they are bookmarking are added and since this whole thing is a social bookmark type of thing, your tags are now shared across the service they've been bookmarked on. I think you can see where I'm going here.