maximillianos - 11:51 am on Aug 21, 2010 (gmt 0)
We use the canonical tag for our mobile pages. To me, that is the perfect use for it. Print pages, mobile pages, etc.
Regarding the quote from the Google engineer who said "slight" differences are okay. That concerned me for a long time until Google finally updated their help page on the use of canonical to include mobile pages. They previously only mentioned print pages in the help section.