As I understand it, the only differences when going upstream (e.g. through Plum Gut against the tide on a rainy Sunday morning) are 1) a difference in apparant wind due to the boat's decelleration relative to the headwind we had, and 2) turbulence in the water.
Everything else is perception. It looks strange, as anyone who paddles up a slow moving river can attest. You feel "caught up" in the current when you turn away from due upstream, and it moves you quickly sideways relatively to the shore.
The shape of a plane circling in the sky (maintaining constant heading change) shows this very well by the shape over ground. If I can find that, I'll post it.
Fun fact #2484: In my avatar, that's DavidPM at the helm of my boat.
Bland, non-political statement goes here.