The World Cup has now kicked over to the elimination rounds: win or go home. If the US wants to get to the quarterfinals, they have to get past Ghana, the team who put them out of the 2006 World Cup. Some people have been spinning this as a revenge issue, but to be fair, Ghana was really only applying the coup de grace in 2006 to a shabby group play effort by the US.
So. Both teams are pretty evenly matched. Ghana has started to improve their defensive play under Serbian coach Milevan Rajevac, and are feeling the motivation / pressure of being the only African team to make it out of group play. So far they've only scored from set pieces rather than open play, but it would be a mistake to assume they'll count on a more defensive style of play for this game.
The US... well, hopefully you've seen Donovan's winner from Wednesday. As a team they're maybe not the technical equals of Ghana, but they are playing well and fast in attack, and if they can remain relatively organized in defense, they've got a puncher's chance. This game could go either way.
One thing to note that isn't directly related to the game: people oversees are noticing, and in a non-patronizing way, that the US public is really taking note of the team's progress thus far. Whether enthusiasm would survive a US loss today remains to be seen, but the US Soccer Federation is making a serious play to host the World Cup again. That's why Bill Clinton is on a charm campaign in South Africa, but FIFA and others are also noticing the ratings in the US and the $100 million that ESPN has spent to cover this World Cup. I don't know what others have thought, but I have been hugely impressed with ESPN's coverage both in terms of quality of commentating and sheer diversity of sources whether online, mobile, whatever. It's been an embarrassment of riches.
So, in the interests of US soccer, another World Cup over here, and just good old fashioned competition, go USA!