I agree with the other commenters here - it can be a bit 'fuzzy', which is disagreeable to people who like definite answers. Case by case is probably a good way of tackling it. The cases, however, do need to be held in reference to the law, and those laws need to be appropriate for the scope and scale of our communication technology.

If we are arguing that someone needs to be 'remarkable' then I'd be interested in what people think counts as remarkable. You may be remarkable in a certain community, job or geography, but not in others.

Exactly. It is similar to "what is 'fair use' of copyrighted material?"