http://joanvinallcox.wordpress.com/2008/10/05/live-blogging-wordcam-day2/
Keeping WordPress Secure - Mark Jaquithmarkjaquith.com
http://markjaquith.wordpress.com/
Upgrades will be automatic, and that will help keep up with security issues.
Top 50 plugins - good security, but less popular ones might have security problems.
WP 2.6 - notifications on plugin upgrades
Themes usually not a security issue, but can be - no system to check yet - again more [...]