Maybe so, but in the past it's been a very good indicator of the outcome of US elections.
This far out, the absolute numbers aren't that important. The interesting information is in the trend -- i.e. how it's shifting from one outcome to the other. And as the original poster points out, it is definitely trending in favor of McCain.
That is very misleading because the bets adjust right until minutes before election day. So, yes the final mumbers are fairly accurate but that does not give any credence to numbers this far out.