Well, most of what FenrisUlf is accurate.
Most pros do use Avids. Very few use Premiere, but some do.
I hate Premiere. When it comes to professional video editing software, it has to be the worst out there. The rising star in the editing world is Final Cut Pro by Apple. It only runs on Macs, but it's a wonderful piece of software and it just keeps getting better and better every year. A system with the right hardware and Final Cut Pro can do just about anything an Avid can do for about 1/2 the cost. The problems arise because all the hardware is 3rd party and it isn't always supported well. Avids are much more stable because they are all created by the same company. There is also the reputation of Avid which comes into play as well. If you are paying a guy $3500 a day to edit your high end commercial, you don't want to see him using a $20,000 Final Cut Pro system, you want him to be using the $150,000 Avid.