I wouldn't go as far as to say AVID is the most used, even among professionals. Maybe the most respected, but not the most used. It fully depends on the project. I hear Final Cut X is great for documentaries and shorter indie projects (I hear it can slow down with longer timelines). Avid is great for work on longer projects such as features.
Most of the higher paying jobs I do are for commercials, corporate gigs, and I'm also doing a documentary. All for various different post houses. And all of them wanting me to use Premiere Pro, which I'm fine with. Premiere is great because it easily integrates with Photoshop, After Effects, etc. So if you're a one man team and having to do your own motion graphics, you can easily go from one Adobe program to another.
But really if you want to be considered a professional editor, you should be able to use whatever you're given. Like sonnyboo said, the program is the brush, not the artist. And Avid may be expensive, but it really isn't THAT expensive. Someone could probably buy all the major NLEs and learn them without too much trouble, if they desired.
Also, Davinci Resolve is supposed to be a full NLE now. I'd be curious to know if anyone has used it for pure editing yet and what they've found.
