I have tried them and they seem like a tonne of fun. I've also been in cities where they are starting to really catch on, and the more people on the bike paths the better! I rode with all sorts of people who may not have felt able to five years ago without eBikes.
I would think they are a great option for anyone who wants to ride a bit faster or further, or over more aggressive terrain or bigger hills than they currently feel able, or want to ride with someone who has better fitness.
edited: removed a word