I've run across a strange conflict between Simple Facebook Connect and Secure and Accessibly PHP Contact Form.
On three sites that I'd recently updated to WP 3.2.1, I was still running SFC 0.25, and v.2.1WP-B20110125 of the form, and things ran fine.
Earlier this week, I updated two of those sites to use SFC 1.0, and a couple days later I realized that the contact form plugin was sending anywhere from 3-5 copies of the end user's message. At Mike Jolley's suggestion, I updated the form plugin to the newest version, v.2.1WP-B20110624, but the duplicate messages problem still persisted.
It took a little more digging, but after I realized that the third site I'd upgraded to WP 3.2.1 had the same form plugin but was not sending duplicate messages, I started turning off other plugins to test behavior, starting with the newest change and working backwards.
When I turned of SFC 1.0 on one of the affected sites, the duplicate messages from the contact form stopped.
I checked the settings for Simple Facebook Connect, and nothing immediately jumps out as something I could change, or that might cause this behavior.
The only SFC modules I have enabled on both sites are "Sidebar Widgets" and "Allow FB Login to Comment". All the others are turned off.
Otto, I can do some more debugging if you need! I love both these plugins, and I'd love to find a way to have them live together harmoniously again :)