Is there any efficient non-linear note-taking software? I'd be interested in tools helping to organize thoughts and ideas, especially in a non-linear way (i.e. not as most existing note taking tools, working with lists and bullets, but rather as a post-it application). Ideally, something like the tool they use in Minority Reports would be cool (without the fancy-touch thingy), but an important point would be the ability to visually connect different ideas/notes together. 

EDIT: Maybe to make things more explicit, I have a visual memory, and it helps me a lot having a graphical disposition to classify things (like important things at the top-right, urgent ones on the middle-left, etc). Basically, I'd like to find my messy desk on my screen :)
Mind maps might be what you're looking for.  From the Wikipedia page:


  A mind map is a diagram used to represent words, ideas, tasks, or other items linked to and arranged around a central key word or idea... Mind maps are used to generate, visualize, structure, and classify ideas, and as an aid to studying and organizing information, solving problems, making decisions, and writing.


There are lots of mind mapping tools out there.  I've used XMind before.  

One drawback is that it's hard to put longer thoughts into a mindmap.