Yes, that's the most common way to do it.
What does the overflow:hidden achieve?
If you have a box with only floated contents, the content (in this case, the floated columns) will hang out of the box. That wouldn't cause you too much troble, but you might have a little trouble getting the top spacing of the footer just right. The easiest way to make the box wrap around the columns is to apply overflow: hidden to it. (It would be a bigger issue if your box had a background color, for example. Without something like overflow: hidden, the background color wouldn't appear, because the box would have zero height.)