Boycott has not done much. To say the Russian boycott of the '84 games was a "success" seems like a bit of a stretch, and to say that the American boycott in '80 was a success has more weight, but is still pretty damn thin. Whether or not it weakened Soviet propaganda efforts significantly is debatable, but what is not debatable is that the athletes who missed their chance there (some their first, some their last, some their only) did not see significant gains. Nor did the American people, who unceremoniously did away with Jimmy Carter's bungling shortly thereafter. Now as for the successes with the South African team, that's something different. There's nothing wrong with the Olympics boycotting a team to show it how isolated it is from the rest of the community, "You're so bad not even the Olympics will accept you." But for a team to say the same thing to the Olympics is completely different. I know that seems like a weird distinction to make, but as to the effectiveness of boycotting, it's absolutely true. It's the difference between a child quitting his family and a family giving up a child. Which one of the two ever has any effect? The child can throw a tantrum, but nobody cares. If the family gives the kid away? That's something serious and irrevocable. China has myriad human rights issues that need be fixed. I mean a bunch; Sudan, Tibet, the Falun Gong, political dissenters, the list goes on and on. But a boycott isn't bringing these problems to light any more than another Beastie Boys concert will.

Protesting is good. It's exactly why you don't boycott. The Black athletes of the Mexico City games wouldn't have gotten the chance to be heard had the US boycotted the games (not that they even had a legit reason to boycott Mexico). But just think how much more meaningful it would be if American athletes, exercising their birth-given right to free speech, marched around the Beijing Olympic Stadium during opening ceremonies with some symbol of protest flying bright and clear for the world to see. It would dwarf any sad protest being held half a world away because the team didn't even make the trip.
All that said, I was a bit surprised to see the Munich murders listed among the "successful" protests. This is a curious, but commonly held belief (that the Palestinians are somehow better off today due to the events of that night in Munich) that I find to be cynical and based in fantasy. Forget about the fact that calling murder "a protest" is in itself a pretty disgusting and cynical appraisal. Even if you think the cold blooded murder of the Israeli athletes to be an acceptable loss (as many surely do) and even if you subscribe to the frankly ludicrous assertion that it put the Palestinian issue at the forefront of world politics (it didn't, it just gave it a mascot), what cannot be denied is that the Palestinian people (not the comfortably compensated thugs and autocrats who have kept them in poverty; I'm looking at you Arafat, Abbas, Hanniyeh, Meshaal, etc.), the people in the street, are not better off due to the Munich murders. Their plight was never brought to the forefront, but instead, the petty race baited power struggle between their thieving leaders and the Israeli government was given some play, the people meanwhile rotted in refugee camps, becoming the world's charity case and a people fully dependent on anyone but themselves to survive. Yeah, thanks Black September, we owe you one.
So in closing, boycott is stupid, protest is not. China is effed up, and possibly, so are the Beastie Boys. The Munich murders were NOT a protest. They were a bunch of people murdering some others. And should never in a million years be compared to the show of strength of those 3 African American gladiators in Mexico City.