And it is a major problem. E.g. a quote from British American Tobacco (http://www.bat.com/group/sites/uk__3...&SKN=3&TMP=1):

Illicit trade is not just the work of small operators. Organised crime is increasingly dominant. The rewards can be high. A single 40 foot long container (8.5 million cigarettes) smuggled into the UK and sold at half the recommended retail price could net the criminals around US$2 million in profit.

and (http://www.ash.org.uk/ash_20gyvtb9.htm):
It has been estimated that illicit trade accounted for 10.7 percent of global cigarette sales in 2006, or about 600 billion cigarettes. This analysis found that the illicit tobacco trade deprives governments of $US 40-50 billion in tax revenue each year, greater than the GDPs of two-thirds of the world's countries.
Source: All Africa, 13 February 2008
Link: http://tinyurl.com/2gqwpm

There is also a global nmarket for counterfeit pharmacuticals. If Afghan Opium was suddenly legalized, it would presumably open up a new opportunity for illicit activity.

P