I thought I would pass this along FWIW.
For years I have wanted to compare a video of my skiing to another better skier, in a side by side comparison, in hope too see my mistakes, (me versus role model at same line length, Pro at ski school, etc.). I briefly looked at Dartfish, but it was too expensive for my budget. I am also somewhat technically challenged, so simplier is better in my case. I recently ran across an inexpensive ($40.00) side by side software called Video Compare. It was developed for slalom snow skiing, but its easily adaptable to water skiing. It has several slow speeds, actual, 0.5X, 0.25X, 0.125X, 0.063X, 0.031X. Or you can pause and forward or reverse frame by frame, which makes synching skiers reasonably easy as long as they are same speed in the course. It is amazing to see what a couple hundreds of a second can mean between a 38 off skier and me at 28 off pass.
It doesn't allow you to save a file, or at least I can't figure how yet, so I can't upload a comparison. But, If you are interested you can see a demo, snow skiing on their web videocompare.org.
Frank Smith - Champions Lake - Clermont, FL