I seldom use bias, but you can use either bias or straight binding with equal success. Bias is more stretchy, of course, and you have to be a little more careful when applying it. As a result, like the others who have responded, I only use bias when I have rounded curves.
Here is a link to one of the best binding tutorials I've found.
http://www.mikidiane.com/f/binding.pdf
Hope it helps!