This is by no means a “top 10″ kind of list for SEO in WordPress but it’s just some of my observations over the years with WordPress.Using WordPress can make SEO much easier, and following these tips will help you get the most out of your WP powered site although i sometimes have been guilty of not following some of this tips myself…:
1. To be sure that you don’t confuse search engine spiders, delegate your posts to only one category.
Comment: This is where i contradict myself as i do delegate my post to a variety of categories, especially when it comes to WordPress Themes
2. To keep your content truly unique, use only the first paragraph of a story on the main index of your site with a link to the full article.
Comment: This is what i do sometimes, and it’s easy to do with the < !--more-- > tag.I try not to do this all the time though as my RSS readers are forced to comeback to the site, but it also helps me to prevent my articles from appearing in full over scrapper sites/splogs.
3. For added site functionality and better search engine spider crawling, use a “Related Posts” plugin.
Comment: You can find the plugins here,
here and here
4. To make your posts more visible to search engines, always use keywords in your titles.
Comment: To get a list of good keywords try the Overture Tool or WordTracker
5. Use a custom permalink structure such as /%category%/%postname%/ for better search engine recognition.
Comment: I think this has been stated over and over again, but it’s still important to implement the Permalinks feature, you can do this via your admin panel >> Options >> Permalink.I personally suggest the use of :
/%year%/%monthnum%/%day%/%postname%/
6. Use a meta tag plugin that allows you to enter custom meta keywords for every page in your site.
Comment: Easy peasy thanks to the All In One SEO Pack
7. Use a social bookmarking plugin to make it as easy as possible for your readers to add your stories to popular bookmarking sites like Technorati and Digg.
Comment: There are tons of plugin out there for this but i suggest Alex King’s Share This Plugin.
8. Create an XML sitemap to make it easier for Google to crawl your site. You can achieve this with one of the many free WordPress plugins available for this purpose.
Comment: Yet another plugin.
9. Use a pinging service to notify bookmarking sites and search engines that you’ve updated your site.
Comment: You can find a list of sites to ping here.
10. Be consistent in your creation of relevant, keyword rich content!
Comment: This is of course easier said than done, it is time consuming and you will need to be knowledgeable about your particular niche, read a lot, visit sites/blogs that are related to your site and try to stay ahead of the pack if you can.
One example is my Transformers sound clip post, although it’s not related to the niche of this blog i can’t begin to tell you the amount of traffic i received for this particular post. 
Popularity: 2% [?]
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I’d like to comment on this point,” To be sure that you don’t confuse search engine spiders, delegate your posts to only one category”.
With all of the talk about themes and siloing for websites, i think it only makes sense to do this with blogs as well. This way there is no theme bleeding.