What kind of storage engine is PlayerPrefs based on?
Is there a maximum number of keys that can be stored with PlayerPrefs?
Playerprefs just stores data in a text document. For webplayers there is a filesize limit of 1MB, but the amount of keys will vary depending on how you name them. Shorter keys would use less memory.
It depends on the platform, on Windows its the registry, on Mac and iOS it uses a plist. Other platforms, no idea.
Not sure if there is a key limit, but I believe there is a 1MB limit.