Quoting my email to different Ubuntu mailing lists:

According to Nvidia, drivers 195.36.08 (i.e. the current driver in the
archive) and 195.36.03 might be affected by the same GPU fan speed
issues which affect the Windows driver:
http://www.nvnews.net/vbulletin/announcement.php?a=39

I have been using these drivers for while now without experiencing
that problem but, if you want to be on the safe side, I suggest that
you temporarily switch to the open driver until we’re sure that the
problem is fixed. In order to do so you can follow either point 1 (the
easy way) or point 2:

1) Disable the driver with Jockey (the restricted drivers manager) and
restart your computer.

OR

2) Open the terminal and type the following commands:
sudo update-alternatives --config gl_conf (and select the alternative
provided by mesa)
sudo ldconfig
sudo update-initramfs -u
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf_old

and restart your computer.

Sorry for the inconvenience, I’ll keep you posted on the issue.