it's possible to assign custom keyboard shortcuts (via system prefs.) to items in the bookmarks bar (menu). as far as i can remember, there was a bug that required activating the bookmarks menu once before the new keyboard shortcuts became usable, but then they worked for the rest of the session. i imagined this was a safari rather than a webkit issue, but as of r25449, the keyboard shortcuts now only work per page load. loading a new page disables the shortcuts until the bookmarks menu is once again activated.
i see, this was caused by r25439. safari 3.04 seems to have fixed this.