Spotify restricts the amount of songs you can skip to 10 in the free version. And next they play you an ad where they stage the (premium) feature of unlimited skipping as some revolutionary game-changer for music players. This anti-feature has literally no other upside for Spotify other than annoying users into subscribing. Which is all completely fair, since it is free after all but I can't find any mechanism which is more to the point of
“Provide incentive for prospects to sign up for freemium but do not provide too much value so that free version of the product is enough.”
I'm on the fence about the assessment of Dropbox as well, it has a load of dark patterns like nagging or bait and switch even and especially for paying users, so I'm not sold it wants to be my friend...