I ended up doing some Cup Stacking activity with her third grade class, and then over the next couple years did an after-school Cup Stacking class in the Spring with the local elementary school. Eventually, I stopped as I had more work and other interests.
Well, apparently Cup Stacking (now called Speed Stacking) is huge. There is a National and World Championships, and an official association (the WSSA). Many schools in the Sacramento area (where I live) participate and even held a competition earlier this year.
I will say that Speed Stacking is a blast and a great way for kids to learn about numbers and patterns and how to get better at something without getting frustrated (this aspect is partially in the approach). It is also very good for hand-eye coordination and thinking with both parts of the brain (since you use both hands).
If you're looking for a fun activity to do with your kids or with a school class, I'd highly recommend it. (Note that thirty kids all stacking cups at the same time is *quite* *loud*.) I also feel like *such* a cutting-edge trendy person for getting into it five years ago! (even if I don't do it much now).