One of my current junior residents is a Mexican national & one of the residents slated to start in 2005 is from Peurto Rico, both of whom attended medical school in their home countries. Both did general surgery @ University programs (Tulane & West Virginia) in the States, got excellent letters of recomendation, excelled on their intraining exams, & had numerous publictions on their CV and they were among the top-ranked applicants on our SFmatch rank lists in their respective years.
So yes it does happen, although it may be a slight negative when your application is reviewed. The bias against an IMG tag can be overcome by training @ a good program & excelling