I doubt that I'm the only one frustrated by web interfaces that require the user to check box after box without providing a "check all" button, but even when there is such a button sometimes you don't want to check all the boxes. Even worse are text boxes when you have to input the same data in 50 places, and if the tab ordering is poor then you may as well shoot yourself.
So why not create a plug-in for a web browser that lets the user select multiple widgets and then manipulate them all at once? For instance, a drag window could be used to select check boxes in a manner similar to how icons on the Windows desktop can be selected en masse. The Control key could be used to add and remove items from the group selection. Once a group is selected, hitting the Space bar could check or uncheck every box in the group. If you're dealing with text boxes, everything you type could be instantly entered into every box in the group. Since drag windows aren't within the current browser paradigm, perhaps the standard text selection-by-highlighting system could be extended to allow for the selection of non-contiguous groups of widgets, and the manipulation could then work similarly as described above.
When I've got a free moment I'm going to look into creating a Firefox plug-in with this functionality.