1.) Add the bookmarklet to your Bookmarks.
2.) Give it a unique name.
3.) Launch System Preferences - Click on the Keyboard & Mouse preference pane.
4.) In the Keyboard shortcuts preference tab, click on the + button.
5.) Select OmniWeb as the application.
6.) For the menu title enter the title of your bookmark (make sure this is exactly the same as it appears in the Bookmarks menu).
7.) Enter your desired keyboard shortcut -- this too needs to be unique so CMD-F probably wont work.