I want an easy put and change orders interface. Of course this would not target those API users but rather the small people who want to toy around with BTC.
I don't trade much but as far as I know on Gox it works like this:
I have 100$.
I put in an order 50BTC@2$.
It doesn't get active cause I forgot about the fee.
I do a second order of 49BTC@2$.
Later I place a third order of 30BTC@3$.
It doesn't get active as I don't have money left so I have to cancel the other offer first.
Putting, cancelling, watching the market ... involves different tools. I use my calculator to somehow put in all my coins/$$ etc. (MtGox got better with that respect I guess).
I would rather want to have some drag and drop interface like this:
Red are my buy orders and blue my sell orders.
I can drag these in from outside and out to a recycle bin.
I am allowed to save invalid/inactive orders (C and D).
If I charge my account, these become active (and visible in the order book).
E and F are in contradiction as they sum up to more than the 20BTC that I have (blue BTC line) so the last of these would be inactive, too.
When I add/move a red/blue order, the lower red/blue line ($/BTC remaining) moves accordingly.
While dragging and at Mouse-Over I would see the exact price and amount.
Mouse-Wheel would allow me to zoom in and further adjust the Satoshis/ct.
I can switch my interface to BTC or $. The above image shows the $-view, so my 20BTC offer @ 4.2something is shown as a 84$ offer.
Finally I can set the interface to instant confirmation or to ask me for confirmation when saving my changes (default).