Comment 19 for bug 455378

@mback - if you still need a workaround
1. install CompizConfig Settings Manager
2. Under the category Window Management, turn on Resize Window
3. Assign your desired keyboard shortcut to the last entry on the Bindings tab, Initiate Window Resize. I'm using <Alt>F8.
Use the keyboard shortcut followed by mouse movement to resize the window across multiple screens. This works for me on 9.10; I assume it would be the same or similar on 10.04.