I play at 1600 x 1024 with eXtreme and I know some play at 1900x1024 or something like that. They normally just stretch the chat window out or add some utility filtered chat windows.
Most people have a set size on some windows because SOE's code will resize them if we don't set them so they can't be resized. Personally out of all the ui's I've used and I keep a current copy of 3 or 4 of the top sets, I couldn't think of any window I would want to resize besides the hotkeys or chat window. Most of the other windows fit into place some how. But each their own
That's what makes this world so interesting isn't it? :P