There are no connectors on the GPIO or on the DSI port. It's all soldering (at least, as far as I know, I would love some confirmation on that). There will probably never be a connector on the GPIO, but the Gertboard will use th GPIO and expand/clone quite a few pins. As far as the DSI (and the camera port) are concerned, I am not so sure, but most of the posts here didn't seem to assume that there would be a connector.
Drawing 700mA off the GPIO is not an option. There's a 1A fuse on the input (AFAIK), USB devices run off the same bus, and the board itsself needs some juice as well. However, you can assume that most custom builds that include a screen would also have some extra 5V lines available, or even some higher voltages at whatever current you specify.
A screen that works, and has soldering instructions, would greatly help the Pi users, and I think that for most people not having a warranty is part of the deal once you break out the soldering irons.