During the "Interactive Site Review" session, Matt suggested investigating the history of each domain name you own or plan to purchase. He suggested avoiding domains with a shady history and dumping domains that appear to have been burned in the past. To investigate the history of a domain, Matt suggests Archive.org. Matt said, blocking Archive.org via robots.txt is a great indication of spam when already suspected.
Matt mentioned speed several times. During the "Interactive Site Review" Matt said that webmasters need to pay more attention to speed. He pointed out that landing page load time factors into AdWords Quality Score and said speed will be a big trend in 2010. During Matt's "State of the Index" presentation, he pointed out Google's tools for measuring page speed and even mentioned webpagetest.org a third party tool. According to Matt, Google is considering factoring page load speed into rankings. Matt said, that Larry Page wants pages to flip for users on the internet. He illustrated this point with Google Reader's reduction of pages from 2mb to 185kb. Nothing official yet but, something to keep an eye on for sure!
During Q&A for "The Search Engine Smackdown" session Matt explained Caffeine as being like a car with a new engine but not an algorithm change. Matt said, Caffeine will help Google index in seconds and that it should be active within a few weeks on one data center. That said, Caffeine won't roll out fully until after the holidays. Matt pointed out that Google is built for load balancing and for that reason isolating individual IPs for Caffeine testing access is difficult. Matt also mentioned that AJAX SERPs and Caffeine aren't related but that Google will continue testing AJAX SERPs.