They were apparently experienced riders (I don't know any of them personally), so all I can say is be careful out there. A report of the incident (I do not consider these things "accidents") made the national press in Canada here, as well as the local press here. An arrest has been made and five charges of failing to remain at the scene of an accident have been laid, with more charges expected. In my own view, the standard of driving continues to decline in North America and it should be far more difficult to obtain a driver's license.
UPDATE: Although four of the cyclists seem to be out of danger, the fifth is in very critical condition and apparently has brain damage. On a positive note, Lance Armstrong, in his daily video from the Tour de France, mentioned the incident after his summary of Stage 16, and sent his best wishes. Although an often controversial person in the world of cycling, he certainly has some admirable qualities off the bike as well.
Tour de France Pre-Stage 16 Update from Lance Armstrong -- powered by http://www.livestrong.com