Walking through my boss' house the only remnants left over from the Super Bowl/birthday party are the helium balloons. Three weeks later they are still doing really well, and flying at the end of their strings'. For the most part they still look full, and not all depressed and wrinkled.
Balloon technology has made real strides from when I was younger. I remember on the rare occasions I would get a helium balloon from someplace, like a pizza parlor. The next morning that son of a gun would be so deflated it would be floating at about half the height it was the night before.I was always depressed at how little mileage you got out of them back then, but now...wow they are great.