The Fifa rankings have been around since 1993, but it's not very clear how much attention people pay them. But if they are going to be used to decide group seeds from now on, everyone take notice, because what happened to France could happen to you next time. In fact, it is already happening to you. These rankings include the last four years of results, so when the next World Cup finals draw is made in December 2013, it will include results from November 2009 onwards, friendlies included. This means that, for example, England have started their race with a defeat to Brazil, and that result will still count in four years' time.
This is where the problems with this system start: had the FA known that England’s position as seeds was dependent on this result, would they have risked playing the world’s number 1 nation? Wouldn't it have been safer to play a lesser team, easier to beat, to guarantee more ranking points? Is this going to start happening from now on, that national teams will start picking and choosing their rivals in friendlies with one eye, or maybe both, on the rankings, looking for overrated teams to beat them while they're still higher up than they should be?
Not all games are worth the same, ranking-wise, and friendlies are worth less than official matches. However, it's definitely a system that can be 'played', in the sense of 'taken advantage of'. Some teams are notoriously over-ranked and at the same time notoriously weak in friendlies played away, like for example Mexico, or Paraguay. They are both tough in World Cup qualifying, but England put four past each of them this decade. If you do that to them when they're ranked 12th or 20th in the world, that will help your ranking very nicely.
This system could be open to more overt cheating, too. A poorer country placed in the 50s, for example, could lure a big team to an away friendly where there would be a "gentlemen's agreement" not to try too hard, in exchange for a glamorous and lucrative visit, followed by a narrow enough victory for the illustrious guests (the number of goals doesn't matter for the ranking, just the win, lose or draw). Won't happen? Look at the allegations of matches bought and sold in Champions League qualifiers and Europa League early rounds. This shouldn't be underestimated.
Answers here or at: