I've just asked the UK ICO for advice and got a confirmation it wouldn't be considered as a data controller or processor. I gave this example:
Me: "Effectively, in my case, the user is adding 'post-it' notes of their own devising that remain 'sticky' so the next time they visit the same page they'll see their own notes - but those notes are never sent to the server"
Me: "It's effectively the same circumstance as a classical computer program being downloaded by the user, and then used (locally) to create/save files on their local device. In that case you wouldn't consider the author of the computer program to be the data controller, surely?"
ICO (Flynn): "Flynn: Okay that sounds reasonable."
ICO (Flynn): "So if your product/service is not dependant on personal data and you are not processing it then you appear to not be captured by data protection legislation."
Me: "Effectively, in my case, the user is adding 'post-it' notes of their own devising that remain 'sticky' so the next time they visit the same page they'll see their own notes - but those notes are never sent to the server"
Me: "It's effectively the same circumstance as a classical computer program being downloaded by the user, and then used (locally) to create/save files on their local device. In that case you wouldn't consider the author of the computer program to be the data controller, surely?"
ICO (Flynn): "Flynn: Okay that sounds reasonable." ICO (Flynn): "So if your product/service is not dependant on personal data and you are not processing it then you appear to not be captured by data protection legislation."