Hey I just saw this message so since no one else offered I can try. I think, when people get offered spots outside the match, that they generally go through the normal routine of applying to schools and going on interviews. If they fit the right characteristics, sometimes places will offer them a spot outside the match. If you have a major "in" with a program, such as doing research there for a long time or major clinical experience, sometimes you can short circuit the whole interview process and be given a position as a "reward" for your hard work, etc.
There are all kinds of programs that give out non-match positions. I know Mayo has done this, MGH. Neither one perhaps this year, but in the past they have. UMass gave one this year to someone switching in after their surgery intern year. I think in general the tougher programs to get into are a bit more stingy with their offers, reserving them only for people they already know well or have some kind of arrangement with. An "average" candidate applying from somewhere else is probably not going to get the same level of interest. You may still get a match position, of course.
I think that if you accept a position outside the match, all that happens is you simply withdraw from the match after the contracts are signed.
I have heard rumors that offering positions outside the match is decreasing, and will continue to do so. Not sure if this is from new regulations or just a higher # of competitive applicants.
If anyone else knows other information, or things I said that are wrong, please speak up.