In terms of seo should my categories, blog roll, latest posts etc columns be on the left of the posts or to the right.
My thought is that if they are on the right then the search spiders will get to the posts and main content a lot quicker as they are not been sent off by any links?
It won't really matter. As long as you don't have any major road blocks (aka coding errors) the spiders will be able to capture all the content and follow most of the navigation structured on your site - no matter where it is. Develop the site nav for the user first. Let the spiders find their own way. Though its probably a good idea to set up a sitemap and use Google Webmaster tools to learn about any issues they might have with crawling. Running the site through a W3C validator wouldn't hurt either.