[akgerber]

I tried a non-powered longboard as a more-compact supplement to a bicycle for city transport. The handling isn't hard to pick up, but riding with traffic is more challenging, especially without a brake. I ended up just sticking with my bike.

These boards appear to have engine braking, but they also note that it's subject to fail on a steep hill or when the battery runs out: http://boostedboards.com/faq/

So— it'd probably be useful for a flattish, quietish commute of up to a few miles where storing a bicycle would be difficult. The learning curve also probably depends on your skills with reading traffic, e.g. if you've biked or motorcycled lately. (Driving helps too but won't necessarily give you an appropriate fear of big busy streets)