I would say, It depends on how much of a gambler you are and where you are flying to, ie. domestic or international. There is a chance that a couple of days before the flight prices will go down because the plane still has seats available. However, sometimes it doesn't work out that way, and the price of the flight could go up.
Chances are very good that you will also get a seat at the back of the plane, and if you're travelling with someone there may not be two seats together waiting for the last minute. This only really becomes an issue if you get travel sickness and require a seat ahead of the wings.
It's always a good idea to look at various airlines and flight deals, and not just watch one. For example, when I flew to Germany in January from Calgary to Frankfurt, Air Canada and Lufthansa were selling the exact same seats on the same plane, but Lufthansa was selling the seats for $400.00 less than Air Canada.
However, you need to watch some cheap travel deals. For example, Cheapoair, will sell you a really cheap ticket, but then they will send you an email (after they take your money) telling you that the seat is no longer available and they apologize for the inconvenience, but they can sell you another seat, at a much higher rate. That being said, they are good at refunding your money quickly if you choose not to buy the more expensive ticket.
There was a study done by Time magazine that found that tickets are cheaper six weeks before the flight.
As well, the cheapest day to fly seems to be Wednesday. When flying overseas anyways. So when you are looking for airline flights, make sure you try out different days of the week.