I have no clue about trading but I wonder if there is some drag and drop interface to place and change orders that would talk to the MtGox API.
I imagine an upper part just like mtgoxlive and below two bars with my $ and Ƀ balances. Dragging within these bars would "grab" the corresponding percentage of my respective balance and allow me to drop it on the market depth above. I would see pins with each of my orders in the market depth so I can drag them back down to my wallet or to some other $ value in the market depth.
I could also imagine this as a paid feature of btccharts.com.
Here is a mock-up:
Notice how the %-values are 0% in the middle and 100% on the outer edge. Reason is that I want this interface to work without having to click again for confirmation and to achieve that, short mouse movements that are more likely to be accidental, should have little chance of ending in a catastrophe. If I drag all my Ƀ and drop them too soon, it's unlikely somebody will snatch them. 2% dropped too soon and being snatched is less dramatic.