Check it out: Escape Pod's blog has just published a post exploding the myth of the deadly flying knife.
I'll admit it - I don't know enough about physics to judge this particular post on the merits of its accuracy. However, I do know enough about the modern fantastic cannon to recall Vlad Taltos's entertaining description of thrown knives as a diversionary tactic; they flinch at the flying bit of pointy steel and miss the larger and more dangerous piece of not-so-flying steel headed for their guts. Or, more frequently, the fact that Vlad is headed for the hills.
Now, I'm much more of a creator of fantasies than speculation, even when I write in a science fictional mode, so I'm quite likely to give my heroes an explicitly magical "get out of physics free" card (I'm looking at you Exalted). I'm about as likely to set up my setting with an alternate physics - Heroic Physics, let's call it - in which throwing knives, swinging off chandeliers, or, say, running on the tops of trees are all possible for anyone.
That said, I like to be specific about where and when I depart from reality. I'd rather sit down to write a story thinking "this story will be set in a setting with general background of Heroic Physics, in which this, that, and the other thing are possible, and characters possessed of certain abilities will depart further in these specific ways" than just make mistakes. In that way, articles like this one are very useful.
However, I also have no problems with departing from reality in this way, when it's done clearly, consistently, and carefully. This is a sentiment it doesn't seem like the author of this article shares with me - she calls throwing knives in general "silly" and "cliched." Different strokes and all that. I can bring my throwing knives along when we visit a world that features Heroic Physics and leave them at home when we visit a world with Conventional Physics. It's all good.