Flare looks to be a pretty awesome library, but it has some issues. The biggest of which is a real lack of documentation written such that a Flex developer could get up a simple visualisation up and going quickly before getting deeper into the code.
So, I've made one: http://simon.oconnorlamb.com/ria/?p=13
And I'm in the process of reworking the interfaces to flare such that instead of having to code renderers for your nodes you can just define a skin (as NodeSprite is becoming a skinnable component).
At least that's the plan. IF it works I'll be writing about that too and posting the modified library…