I don't use any sort of SEO plugin, I just modified my own theme to include all the bit I wanted. I suppose those plugins are quicker, but they're less precise, in my experience.
IMO, Technorati sucks. Big time. It never works properly, and it's basically useless when it is working. Don't bother.
Pretty permalinks are nice, but I don't think they help SEO in particular. Maybe a little, but very little.
The most important thing of all:
MAKE YOUR SITE VALIDATE!
No question about it. Valid sites get such a huge boost it is unbelievable. Valid sites parse easier, index better, and generally work better all around.
If you're "close" to valid, then that's okay too... but if it is possible to fix a validation problem, then do it. It can't always be done though. Imagemaps are a problem (there's no valid way that works in all cases for them), and I use the embed tag in XHTML because it works better on certain browsers, but other than that, all my sites are wholly valid.
Second biggest thing you can do: Use semantic markup. Headers should be in H1-H6's, not styled DIV's or P's. Main text should be in P's. Lists of things should be in UL or OL's (and a sidebar of boxes is a LIST, even if you don't think it is... So is a navigation bar going horizontally... describe the items, worry about positioning them correctly later). That sort of thing. Stuff works way better when you use tags for what they were meant for.
A corollary of this is: If you want to change how something looks, then you edit the CSS. If you ever edit the HTML to change the LOOK of the page, then you're doing it wrong. Hell, if you use *style* attributes anywhere in the HTML, then you're probably doing it wrong (certain exceptions are okay). If you have class names like "red" or "bold" or even "center", then you're doing it wrong.
The (X)HTML markup should make total sense without any styling applied to it at all. Every classname, every id should identify the thing it contains, not anything *about* the thing it contains. Save the looks for the stylesheets.
Third most important thing: Have good original content. Only you can write content. Do it well.
Do those right, and you're well on your way to high pagerank.