Blogs are in theory very search-engine-friendly. They are the perfect format for adding new content often, and search engines like that. Also blogs have many built-in features and settings to make them easy to crawl and index by search engines.
Blogs have search-engine-visibility settings, for example the WordPress software adds or removes a
noindex,nofollow meta tag to the HTML
head element of blog pages according to this visibility setting. A noindex,nofollow meta tag makes a page invisible in search results, prevents search engines from adding a page to search results. But for that the page has to be accessible to search engines, not blocked in robots.txt file. If a URL is blocked in the robots.txt file, search engines do not access it, but the URL still appears in search results (only the URL, no title or snippet), if search results collected that URL from links or XML sitemaps.
Another feature important to search engines is the URL structure. Blogs software provide settings for that, for example in WordPress gives the option, in Settings>Permalinks, to have a user-friendly, search-engine-friendly URL structure, like http://sitename.com/blog/2009/08/03/post-title-excerpt/
The URLs of RSS feeds automatically generated by the blog software, that include recent posts, can be submitted to search engines like Google, Yahoo, MSN, Ask, as XML sitemaps, and added in Sitemap lines to the robots.txt file, to quickly let know search engines of the new URLs of the blog, and help with indexing in search results.
It is very important to have indexable URLs easy to find by search engines, but as important as that is to stop search engines from crawling and indexing duplicate content URLs, from presenting to search engines a quasi-infinite space of URLs. For example the search feature or category navigation generate URLs with similar content as the blog pages, and it is good practice to block these URLs in the robots.txt file.