Details

Username enumeration (from author querystring and location header)
Weak password cracking (multithreaded)
Version enumeration (from generator meta tag)
Vulnerability enumeration (based on version)
Plugin enumeration (2220 most popular by default)
Plugin vulnerability enumeration (based on version) (todo)
Plugin enumeration list generation
Other misc WordPress checks (theme name, dir listing, ...)

Download
http://code.google.com/p/wpscan/
http://wpscan.googlecode.com/svn/trunk/