As with any content management system, Drupal can throw up some interesting search engine optimisation issues that you need to be aware of, especially duplicate content problems which can come about due to Pagination of your blog and taxonomy pages and views but also you can create duplicate content issues if you use a lot of tags and only tag one but of content with each tag.
Here's a few modules that can really help with your on page content optimisation and general SEO issues:
The first one is Content Optimizerwhich requires another module first - Content Analysis - this will give you on page optimisation tips, showing if your keyword density is right and whether your meta tags are set-up for the correct search terms.
Another nice looking module is Drupal SEO Friend which also gives a detailed breakdown of your website's SEO set-up.
Best of luck with the SEOing people! Now that we've all survived the Panda and Penguin updates, we're ready for anything! :)