For a little more Google opinion/policy:
Google will more at cloaking in Q1 2011. Not just page content matters; avoid different headers/redirects to Googlebot instead of users.
For a good opinion piece with term explanations:
Cloaking is good for you, Sebastianís Pamphlets, 05-July-2010.
Frankly, I would appreciate some more detail from Mr. Cutts now that he has shocked the SEO troops. That tweet was too much like 'Google will be more at fire...'
Obviously their last algo change to combat cloaking has been defeated widely enough to be of concern to SERP/AdWords quality - and not just webdevs
Expect to hear of false positives as innocents again get dumped along with a few blatent transgressors (not including any G service partners). Do I sound cranky? Must be the eggnog.