The control is quite good at the moment but as of the CTP release it is missing quite a lot of goodies. Listed below are some of my suggestions for the control.
1) Double clicking at the top of the control should make it expand full screen. Similarly double clicking at the top of an already fully expanded window should make it go back to its normal form. Hope im making sense here
2) Possible docking areas for the control?
3) Ability to easily open the window on clientside and server side
4) Position the dialog at certain parts of the screen. For instance I would like to set a dialog to appear dead center of the screen or even change it to appear at the bottom right.
5) Loads of skins especially Vista and office themed skins.
I'm not sure if this should be #8 or #9 since there's two #7's :)
I would like to see the ability to include an icon such as the "!" or "Stop" or "?" or "Information" icons you can display in a standard windows pop up dialog. I guess the best way to implement this would be to allow us to specify an image of our choosing to be displayed. That way we could display a big red X for an error and a big green check for non errors, etc.