I haven't looked into outliners much recently, since the microblog saga, but I have recently been playing with freemind which is more of a brainstorming tool than an outliner.
Bullet review:
- written in java i.e. it's slow to boot up and uses lots of memory (i.e. lots of swapping on 256M system). Performance is ok once it is running.
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Nice graphical display: the idea is that it is highly graphical to appeal more to the right side of the brain which likes pretty colours.

- The graphic above was generated using a simple 'export as jpeg' option.
- The map acts like a huge canvas. You scroll around the canvas by clicking and dragging (as per google maps) so you don't need to use the scrollbars (very nice).
- Very responsive on the keyboard: return key to start new sibling which is more intuitive than it sounds. This would make it quite quick for note taking and it could be driven without the mouse.
- Nodes can link to web pages, disk files etc. Annotate your hard disk!
- It saves maps in XML format. There is potential here for generating maps in software for display.
- maps can be put on the internet read only either as html (without the graphics, just trees) or graphically if the browser supports java.
I like to do these kind of diagrams for brainstorming so I may stick with this.

