The first problem with rankings its not the best team at that moment its who is having the best overall season. One example is a few years back when Georgia in football was widely considered to the be the hottest team in the country and would have beat anybody in football. But because they had lost earlier in the season they ended up playing in the sugar bowl against an ranked and highly overrated Hawaii team. Which they stomped.
The next is a team like George Mason which had that great final four run a few years back. It was highly criticized that they even got into the tournament. Then the only preceded to beat the likes of Michigan State, North Carolina, and UConn. Eventually losing the Florida who went on to win the NC. You can also look at Davidson in 2008 going to the elite eight as a 10 seed and they should have beat Kansas in the game that would have got them to the final four. Really rankings are all related to perception. A lot of it goes into the rankings of other things too such as recruiting classes. Kansas state was a ranked third in the preseason, went on to fall out of the rankings, and then beat Kansas, who had just become number 1. Many teams have been ranked and just not soon up in bowl games and NCAA tournaments. Just based on a biased opinion of their league. Just look at the Big Ten in Bowl games.
There are teams like Utah State who consistently win tons of games. But they haven't won in the post season since an upset of Ohio State in 2003. I love the aggies but they are a classic overrated team. They beat a lot of bad teams and are still good but its unlikely that they will even get the respect of a 24 ranked team on seeding or even win a game no matter what their seed is. Honestly I think BYU is another example. Yes Jimmer has been amazing. But honestly besides SDSU and Arizona they really haven't beat anybody. They've had Arizona's number for awhile and frankly that arizona is different from the one we are seeing right now. SDSU great team but they only beat a Gonzaga team that isn't even going to win its conference, and is behind a team that just lost to team with only 5 wins.
So really do rankings mean a lot no. I do believe that we should keep them. But do they determine if a team is good not really. It comes from the tendency to overreact to the losses that many good teams have. You can't win every night. Just because you lose once does that mean you are no longer the best team. no it doesn't. The problem is losing your ranking can get you out of a national championship. Which is really the problem with the BCS. You can't argue with the playoff system of march madness, you get your chance to prove yourself. That is if you get into the tournament.