How drugs enter the US depend on the drug. The DEA estimates that 90% of Marijuana comes in from Mexico, while Cuba is the big importer of Cocaine, and Chinese mafia accounts for most drugs such a GHB.
Here is the DEA's reports on smuggling (and people do find new and interesting ways everyday)
http://searchjustice.usdoj.gov/search?q=smuggling&q=site%3Awww.usdoj.g ov%2Fdea&sort=date%3AD%3AL%3Ad1&output=xml_no_dtd&ie=iso-8859-1&oe=UTF -8&client=default_frontend&proxystylesheet=default_frontend&site=defau lt_collection
http://www.usdoj.gov/dea/concern/18862/index.htm#Summary




