Cable ski has quite a big impact in terms of trying basic skills which you can't do behind a kite initially.
As a beginner, it helps with basic riding skills, balance, powerslides etc.
Intermediates can practice backside powerslide, blind 180's, 360's with a handle pass, toeside riding etc.
Advanced riders can practice things like backrolls, KGB's etc if you're into wakestyle tricks, otherwise, its fun for just playing around.
If you want to do good inverts, a wakeboard is a requirement as the bindings are necessary, and you need the wakeboard rocker for loading the cable on releases.
I put together an article on this recently for a website with video clips etc. You can check out the article on
http://www.ikiteboarding.com/article_detail.aspx?id=68 . Its still missing some of the clips and I haven't extended it to add the inverts yet, but I'll be added them shortly. Part 1 is an overview, part 2 is a short overview on the differences between wakeboards and kiteboards, and part 3 is a how to do tricks thing with the basics from launching to small tricks.
The article is primarily aimed at beginners, but I rate the place as good fun when there is no wind around. Its also good fitness practice as your arms take strain and its a good overall workout.