I spent 24 hours in Paris on the 17th and 18th of January.
In the late afternoon/early evening of the Sunday, I spent a little time at Gare du Nord and had no bother. I then spent well over an hour at Paris Est, using the tripod at both the buffers and country ends of the station and wasn't hassled at all. That said, I was careful not to get in the way of anyone. I also saw a couple French lads taking pictures with a tripod.
On the Monday, I spent a little time at Gare de Lyon in the morning peak and had no bother - using my tripod for a shot at the country end of the station. Later, I spent a little time at Austerlitz and took a couple of photo's without any problems. At Montparnasse, I didn't bother taking any pictures, as the place is pretty rubbish in that regard. St Lazare was the same as Austerlitz and I had no bother at Gare du Nord (again). Likewise, I had no problems at any smaller stations outside the centre/city.
I didn't attempt any photography on the Metro, so can't help there.
I think it is worth being sensible and considering your surroundings, but the only hassle I got on this trip was at Kings Cross, where a self proclaimed jobsworth told me I couldn't use my little tripod, despite not being anywhere near other people! Welcome home, I thought...
Security levels are still very high; discretion would be the order of the day.
Legal lineside locations might be better at the moment?
I remember those security heavies in black bomber jackets (no fluorescent jackets then!) talking with us on a Metro station way back in 1994!