Pandora
Jeopardy (which I played often for a while, but then stopped)
Some Bed Time story skill, which is awesome and hilarious and I should know what it is so I can recommend it.
Nest, which never worked because I guess you have to use Heat/Cool mode on your thermostat which is dumb.
I think probably:
1) I installed more skills than the average user on initial setup (expected median: 0)
2) Most users open the app at a similar frequency to me.
3) The primary use of the device for most users is music.
4) Some people don't use them at all after the first week.
As far as development of skills, I know at some point they were offering "Amazon Swag (apparel)" in exchange for uploading your first Skill. Come on people, I've got mouths to feed here!