Should I include my logo text using ‘alt’ or CSS hiding?

Matt's answer:
CUTTS: Okay. Richard M. from Australia asks, “If you have a company logo on your site, what is the best way to include the text of the logo for SEO purposes? ALT tag, CSS hiding, or does it matter?” Yes, it does matter. It’s much better to use an ALT tag than to use, like, “I’m hiding some CSS,” you know, nine thousand pixels over to the left of the web page or something like that. That’s what the ALT tag was more or less built for, you know, or ALT attribute, you know, or however you want to say it. But, yeah, go ahead and use ALT and that’s a fantastic way to say, you know, “This is the text that’s in my logo,” search engines can read that and use that. I would not, you know, hide it using CSS or anything like that when there’s a perfectly valid, perfectly simple way to do it. It does the job just fine.
by Matt Cutts - Google's Head of Search Quality Team