In the US, Gallup have just released the results of their October crime poll, the long term trends are striking:

U.S. Support for Legalizing Marijuana Reaches New High

Majority in the West favors taxing marijuana sales to boost state revenues
by Lydia Saad
October 19, 2009

Gallup’s October Crime poll finds 44% of Americans in favor of making marijuana legal and 54% opposed. U.S. public support for legalizing marijuana was fixed in the 25% range from the late 1970s to the mid-1990s, but acceptance jumped to 31% in 2000 and has continued to grow throughout this decade. (more)