Software

Yeah as Grady pointed out, depends on how much money you have. But Blender surely is used widely, sometimes you hear about it, but most of the time you probably don't. Things are rapidly changing though, you never know if the surge in Blender is going to go up even faster than it already has. But it's important to remember, these are just tools, the artist wielding them are the ones that make all the difference. The more you use different software's the more you realize you don't really need X software to get the task done, that are all tools just like a hammer is a hammer. They have their different advantages here and there, but the quicker you become a software agnostic, the better. 

I agree with Omar and Grady, for the most part. I've been compositing on feature films for about 24 years now, and sadly, I've never seen anyone other than myself using Blender's compositor as the compositing tool. And I've only used it on freelance independent movies, not big Hollywood productions. It's still lacking a lot of pipeline tools, not to mention basic compositing necessities. For example, a pipeline tool it could really use is better, easier tools for loading in LUTs and various colorspace in the actual node tree. And an example of a basic necessity is being able to cache your work for realtime playback. There are work arounds for these, of course, but things like that are what keep it from being used as a compositing tool for teams.

And that's not even mentioning awesome tools like splinewarping, smart vectors, optical flow retiming, intuitive planar tracking and corner pin tools, etc.

I'll take a guess as to Sean's answer. (In Sean's voice) The community, Blender is awesome, not just because it's free, but in being open source and the community making so much inputs, makes the software have a life of its own. It's versatility and customizability and great, but again, the community makes it shine, because it's ours. When you're using it as a standalone artist it is really powerful, it's just for working in a pipeline that is more lacking. Well, I'm off to working on some more Hollywood movies, it's not as dramatic as it sounds though, delivery times are crazy, people want things so ASAP that ASAP is too short of a time. I'm saving up to buy a farm and get a more quiet life because this industry is too draining. 

Hahahaha, excellent answer, Omar!

Sorry, I've been moving! not to that mythical farm, but across town!

And Omar's answer actually isn't spot on for me. It's definitely why I stayed with Blender, though. The community is just amazing.

However, sadly, I actually did start using it because it was free. I was working at a big studio, and to make vfx elements for myself, I would have to go home, do it in 3dsMax, email to my work email, then the next day I could start using it. If I had to make a change, I had to wait until I went home. But our work computers had Blender installed already (it was v2.48 or something like that), so I started messing around with it because it was there. As soon as 2.5 came out and overhauled the UI, I was really hooked.

And back then, for all the freelance jobs I would do at home, I used After Effects for compositing. But I wanted a node compositing program like I was using at work, and Blender had it. When Adobe went to subscription, I stopped upgrading all my Adobe products. And sadly, there's still not been much development in free or open source compositing programs. Fusion is great, and Blender is great. Blender's compositor doesn't get as much attention as the other areas of Blender, but I'm very glad we have it.