- Use xf86-input-mtrack
Debian Jessie (w/ gnome3) uses the "synaptics" xf86 input module as a default. It is very precise but doesn't support "resting thumb" behaviour that you're used to from OSX.
xf86-input-mtrack is an enhancement of xf86-input-multitouch which is configurable. I built it from source from here: https://github.com/BlueDragonX/xf86-input-mtrack But i see that it's also in the debian package repo. So you probably only need to do:
sudo aptitude install xserver-xorg-input-mtrack
I created an override config in /etc/X11/xorg.conf.d/50-synaptics.conf (create the directory if it doesn't exist) which looks like this: