While it is perhaps somewhat cosmically funny that these allegations of bribery to get Kilrea to drop out at the same time both the NDP and Paul Martin apologized to David Oliver, I do wonder how dedicated O'Brien really is to staying on.
This is a situation which could rapidly worsen, even having federal implications for the Conservatives, as the Liberals are alleging that John Baird, (who is currently off sinking the Bali conference: http://www.theglobeandmail.com/servlet/story/RTGAM.20071212.wbaliyork1212/BNStory/International/home)
may have been involved. Obviously O'Brien has to say he will stay on at this point, lest he appear weak and scared, but I would not be surprised at all if he were to step down if this affair becomes worse, particularly given O'Brien's relative unpopularity.
Simply on a rumour mill note, I have heard from various places around Ottawa that Jim Watson, the former mayor of Ottawa, current MPP for Ottawa West-Nepean, and Minister of Municipal Affairs and Housing, may have more than a fleeting interest in having his old job back. Watson's name is sometimes thrown around with those of Smitherman, Bryant, Duncan, and Bentley as potential leadership candidates, but given O'Brien's tailspin, I wouldn't be surprised if Watson threw his hat into the mayoral ring.