I know exactly what you mean. I live in PA and we've had summer like weather in March. Our falls don't always cool down like they used to anymore. I used to look forward to nice cool weather in late September, but in recent years that hasn't really happened until late October/early November. I guess the problem is global warming.
Global Warming IS the culprit, it's just that so many people out there refuse to accept it, simply because of Al Gore (I swear, if Bush said the same thing, we'd all be doing what we could to prevent any further Global Warming from happening).
This year, I think the entire country was experiencing unseasonably warm weather this March. Being down here in the south, much of the month of September is still pretty hot for us, but USUALLY, October's kind of 50/50: half of the month is still pretty warm, but more spring-like warm rather than summer-like hot, while the other half is cool enough to wear long pants, but not quite chilly enough to warrant a sweater or anything, but November usually marks the beginning of sweater-weather (which I LOVE).
Again, that's usually, but the last couple of years or so, that hasn't quite been the case.