I was in the 4th and 5th on foot this evening..nothing. Nothing as far as the could see from just east of the Notre-Dame to the south. It was much more isolated then anyone imagines.
It was only in the 4th and 5th during the protest march... it's certainly not in most areas, you're right. You might want to avoid the area around the Sorbonne, though... not far off the Latin Quarter. The CRS (the serious cops) are not in the mood to play games. :-) Enjoy your visit! Hope you took advantage of the sales last week!