As far as I know, there is no specific problem with RER line B between CDG and Paris Nord (Gare du Nord) at the moment. I take this train every other week and will continue to do so. However, if time makes it possible, I select non stop trains between CDG and Gare du Nord.
You're more likely to face traffic disruption due to technical reasons, including a potential strike when RATP staff have been attacked. That was just the case last week and trains to CDG where not connected to the line B southbound traffic (the now famous
'interconnexion suspendue à Gare du Nord'). Trains to CDG temporarily departed from the surface station.
Update:
http://www.ratp.fr/
(click on 'trafic' on the left). Very useful (there are about 10 metro stations currently shut down during works).
Air France coaches are a little bit more expensive (€12) but perfectly safe.