Cloakers beware! Google plans on investing more time and energy into anti-cloaking efforts in 2011.
Cloaking, for those of you who aren't familiar, is the practice of providing one piece of content on a web page for human users and another piece of content for robot agents. The goal of cloaking is to offer web content that Google will find delicious, but trick unsuspecting users with an alternate fare. The practice is widely viewed as deceptive and is often times used as a process to disseminate spam or build false search rankings for websites.
Specifically, Google warns that they are going to be focusing on various types of headers/redirects to Googlebot instead of human users.