Here's a pretty fervent plea for boycotting the 2008 Olympics in China. It's based on a necessarily biased paper issued by the Falun Gong, and so it's hard to tell from this one blog entry alone whether things in China are as bad as stated.
Not only is China bankrolling Darfur’s Genocide; for more than eight years it has sought to eliminate Falun Gong, which in 1999 had an estimated 70 million practitioners in China; it has likewise abused democracy activists, lawyers, human rights defenders, religious leaders, journalists, trade unionists, Tibetan Buddhists, Uighurs, ”unofficial” church members, and political dissidents.
I've read of these particular accusations on numerous occasions, and so I would tend to give them some credibility. And, at least some in the US government agree:
All of these reports culminated, on August 3, 2007, in Congressman Rohrabacher introducing House Resolution 610 , aptly named because the “610 Office” in China is an extra-constitutional agency established by the former leader Jiang Zemin. It was specifically created to persecute Falun Gong and has absolute power over every level of the Communist Party and all political and judiciary systems.
Rohrabacher’s H.Res. 610 expresses “the sense of the House of Representatives that the United States Government should take immediate steps to boycott the Summer Olympic Games in Beijing in August 2008 unless the Government of the People’s Republic of China stops engaging in serious human rights abuses against its citizens and stops supporting serious human rights abuses by the Governments of Sudan, Burma, and North Korea against their citizens.”
Rohrabacher proclaims, “In 1936, Nazi Germany hosted the Olympics giving Hitler a worldwide platform to showcase his fascist propaganda. It was wrong to support the Olympic venue then and it’s wrong for the United States to support this prestigious event being held in a similarly fascist regime in 2008.”
Communist China lost its bid for the 2000 Olympics because of its horrific human rights violations. Recognizing this concern, the Chinese regime explicitly promised to improve human rights  in order to win the 2008 Olympics Games. Its subsequent record belies its empty promise. Human rights in China have not improved; they have grievously deteriorated.
Ultimately, I think I would support such a boycott, although, like Carter's boycott in 1980, I don't think it would have much effect. And as I think about the whole thing, it strikes me how much of a free rein China receives in the mainstream media for its human rights violations vs. its economic policies and product safety issues. Hmmm.