I've always found the Olympics interesting and in soccer the games have historically been very unpredictable. There are many nations that have never played a World Cup game, but have qualified for the Olympics, and the traditional soccer powers don't always do as well in the Games. Here are some details about Olympic Soccer.
Up until and including the Seoul 1988 Olympics, the event essentially used full national teams without restrictions. Since the 1992 games in Barcelona the event has been a U23 event. Since the Atlanta games in 1996, nations are also allowed to pick 3 "wild card" players that are over the age of 23.
Number of Qualification Spots per Continent - Beijing 2008:
4 - Europe
4 - Asia
3 - Africa
2 - North America
2 - South America
1 - Oceania
China automatically gets one of the Asia spots
Final Four Nations in Recent Olympic Games:
Gold medal winners in Bold
2004: Argentina, Paraguay, Italy, Iraq
2000: Cameroon, Spain, Chile, USA
1996: Nigeria, Argentina, Brazil, Portugal
1992: Spain, Poland, Ghana, Australia
1988: USSR, Brazil, West Germany, Italy
1984: France, Brazil, Yugoslavia, Italy
1980: Czechoslovakia, West Germany, USSR, Yugoslavia
1976: East Germany, Poland, USSR, Brazil
Soccer "Powers" that have appeared in past Olympics:
Listed by current FIFA rankings
192 - Afghanistan - 1948
171 - Chinese Taipei - 1960
165 - Malaysia - 1972
161 - Netherlands Antilles - 1952
157 - Burma (Myanmar) - 1972
127 - El Salvador - 1968
107 - Sudan - 1972
103 - Syria - 1980
Between 1952 and 1972, Hungary was without question the powerhouse of Olympic soccer. They picked up 3 golds, 1 silver, and 1 bronze medal out of that stretch of 6 olympic games.
Since 1980, only Brazil, Argentina, and Spain have won at least 2 medals of any color.
Cameroon and Nigeria make it 2 African nations with Gold Medal wins in the last 3 Olympic competitions.
For some interesting discussions regarding the US team selection, check out these posts at Soccer By Ives and Soccer Insider.