Fellow coworker Jeff Hodges has announced the formal specification draft for Strict Transport Security. STS is a new proposed protocol for allowing a website to instruct returning visitors to never visit the site on http, and to only visit the site over https and is entirely opt in. This can prevent MITM situations where an attacker can sniff or inject content into an HTTP stream, and can only be set over HTTPS.
If you're into bleeding application security research/work this is worth checking out.
STS Specification: http://lists.w3.org/Archives/Public/www-archive/2009Sep/att-0051/draft-hodges-strict-transport-sec-05.plain.html