Microsites can still be powerful additions to your business’ web presence.
However, they can also cause you some serious headaches down the road if implemented incorrectly in 2013 (Google is an evolving beast).
Rand’s video from 2009 still rings true:
Additionally, go read his description of “subfolders” vs “subdomains” for more info on the topic.
We’ve done a great deal of work with clients on microsites over the years and are always astounded when people within the SEO industry confuse the subject to the point of actually hurting a client’s optimization. Always do your homework and always make sure to ask lots of questions about implementations and long-term strategies.