I have had some experience skiing in current and also have had many philosophical conversations about what happens when skiing in current. Here are a few of my thoughts:
1) It is easier to run your hardest pass upriver.
2) The current is much more pronounced than a wind, but harder to sense because you don't feel it like you do the wind. Though again, I feel it has more of any impact than the wind.
3) Upriver feels more stable, earlier, wider, and easier to maintain a tight line. Downriver it feels unstable since water speed under the ski is slower, thus you tend to river deeper but yet faster and it can be difficult to stay early and wide because of this.
4) I personally switch my ZO setting upriver and downriver. I like a C1 up and a C3 down. I would rather take throttle out of the ball rather than into the next buoy since it is much more difficult to initiate and finish the turn downriver.
I also agree with the description @6balls mentioned earlier.