Use of "Serializable"

Many classes are declared to be Serializable. But in effect they are not because some of their fields are not Serializable (this is reported by "soundcloud.io").

In my opinion, the

implements Serializable

declaration must be removed from all classes but those explicitly designed for persistence. Actually, even for those, I'd favour a design where persistence is implemented "externally" (i.e. not by Serializable).