Matt Cutts, the Google engineer and public face of the search engine's spam-fighting team, has posted some SEO tips for bloggers that he first shared in a WordCamp 2007 presentation last month.
He's posted his presentation deck, a link to a video and transcript, and links to write-ups of the sessions, so you could conceivably spend the rest of the day today just consuming Matt's words of wisdom in various forms.
He also clarifyies the reported news that underscores are now the same as dashes to Google:
If you read Stephan Spencer's write-up, he says that underscores are the same as dashes to Google now, and I didn't quite say that in the talk. I said that we had someone looking at that now. So I wouldn't consider it a completely done deal at this point. But note that I also said if you'd already made your site with underscores, it probably wasn't worth trying to migrate all your urls over to dashes. If you're starting fresh, I'd still pick dashes.