Slightly different reasons for me.
I'm an avid mountain biker, and have a good level of fitness already, however for me a lot of the fun is the downhill sections of the trail.
Generally, a typical ride will be 50% up, 50% down in distance, but 95% up, 5% down in time. I wanted to change this so that I could go faster on the ups, allowing me to do much longer routes with more downhill fun!
My Crystalyte kit arrived yesterday, and I've booked tomorrow off work to get it all running for the weekend!
I would also like to cycle to work, which I used to do but my workplace has relocated an additional 10 miles away (now 15). I can do it, but don't want to get all sweaty before I sit at my desk!
If the e-mountainbike is a success, I'll get another kit for my road bike (minus battery - both bikes will share one).