Does anyone else have this problem and know of a work around?
On a WebPart page, add a Search Box WebPart. Edit the properties of the WebPart and change the Query text box width (in pixels) option. I tried setting mine to 50, 300 and 500 and none of these values seem to change the way the text box looks on the page.
It seems the Search Box WebPart doesn't honor the value set in the TextBoxWidth attribute. Sometimes I feel like I'm a beta tester on a released product...