Originally Posted by Teon

Yup. I always keep some old shifter and brake cables around for just that purpose. Just slide the appropriate cable in to the housing in the area you're going to make the cut, and cut quickly. The cable helps the housing retain it's shape,(or, in technical terms, the housing doesn't get 'mooshed' ) and if you have a decent pair of cutters, I have found that 80-90% of the time you'll get a nice clean housing cut that you don't have to file or mess with. Believe I learned this trick from Thrifty Bill awhile back.

Although Robbie is also correct.....it's still a good idea to debur it, even when the cut looks clean. For that I usually just stick one prong of a needle nosed plier in the end and rotate it a few times.....seems to take care of any sharp edges.