When someone picks a blogging service, what often determines which one they'll pick may be the price or features. However, reliability is often forgotten, despite the fact that if your site goes down, nothing else really matters. Pingdom, an Internet monitoring company, published a study they did of some of the most popular blogging platforms on the Internet. The study was conducted over 2 months, and covered the services from Tumblr, Wordpress, Typepad, Blogger and Posterous. They used in-house software to monitor uptime, and check the availability of certain services. Overall, they found that during the period tested, Tumblr was by far the most unreliable, with Blogger being the winner at basically no downtime whatsoever. Check out the report for full details.