I just saw my first game during these Olympics, when I watched Portugal get humilliated 2-4 by an excellent Costa Rican side.
The quarterfinals for August 21st are as follows:
As compared with other tournaments, the interesting teams are Mali, Iraq and Australia, who have an otherwise lacking appearance in World Cups (Iraq in 1986, and Australia in 1974).
In spite of the surprises seen so far, I think Argentina stands the best chances of winning. They have many young super-stars as D'Alessandro, Saviola and Tevez, well supplemented by older players like Roberto Ayala and Gabriel Heinze.
Paraguay also stands good chances, as they have shown amazing strength so far. It is becoming interesting to follow.