Firstly (and before I read all these awesome responses) thanks so much for doing this, Kirra. 

Now - readity I go: 

I used to (many moons ago - or years) GM and play bulk stories. Back when I had the time to devote. At that time, I don't recall worrying overly much about NPCs. There was open discussion on this or that NPC and generally, we went with the name/nameless manner Arsenal stated. If a named NPC was to be used, generally someone said "Go ahead and move the mermaid" or "I'm just tossing Mr. Grand in there, anyone can push him." 

At this time, I'm no longer GMing and I've all but relegated myself to the two person RPs (easier to discuss time away and much easier to pick back up the muse when the story had to wait for your house project). So I'll take on the questions from that POV. 

[quote=Kirra]
What is your take on an NPC? How much of an importance should be put on them? How should an NPC be dealt with in the IC and who should be able to control them? GM/roleplayers, what has been your experience with NPCs and what has worked best for you in the roleplays you've been in? How is a good NPC played?
[/quote]

I LOVE NPCs.. love, love, love them. I love keeping characters out of a vacuum. There is a wonderful way of looking at each one of us where there are bits and pieces of ourselves we are aware of and not aware of, that others are aware of about us and not aware of about us. The intersections between these bits and pieces are where NPCs bring the world and one's characters to life. In a world created by only two people, NPCs become essential. The world is plain and juvenile without them. 

As for control, I generally leave that up to whomever I'm writing with. If I write with people who need to control their NPCs, then that's easy enough to allow - provided I can do the same. Now and again, someone will want full open reign on any NPCs and that can be fun as well. Generally, it's a balance. One can almost sense when an NPC is too important to muck with. They "feel" important and until they are offered up on the alter of The Story for all writers to play with, they remain in firm control of their creator. 

I suppose I've not changed from when I GMd way back when. It seemed then like whatever my players were comfortable with - with the most sensitive of bars being the one everyone else had to live by. The more open and collaborative writings were always the more rich, but it definitely took a lot of give and take to make things work. People had (and still have) to not be so tied to any one outcome so that the creation could be more mobile. Because when you got's it right, it's purty cool. 

As far as how a good NPC is played, I've always lived by the demands of the story. I love that NPCs can be an important character in disguise, the writers just need to find it out over the course of the creation. One of my favorite characters was a woman I set up as a black market transfer only. The minute she hit the page, I realized she had a life of her own - even a story of her own. She superseded the main characters and it was beautiful. But then, she was also just what the story needed and her insertion gave the story the key to a perfect climactic ending, complete with happy rainbows and unicorns and love riding off in the sunset. 

Therefore, a great NPC is one who fits the demands of the story. If this is that proverbial baker without a name and the town crier and the man at the job board who has the cybernetic eye or if it is the girl who is named Marybeth and has a long history with Bob and knows just what to say to get him to lob food at her head because the pair of them lived in that Horrible Woman's Orphanage together and they survived beatings by flinging themselves before switches and they've exchanged blood like blood brothers - then so be it. Giving the wrong NPC power frays the story and keeping NPCs bland just stifles the story. It's a nice balance, ain't it? :)