Experience: 

Sweden has a perpetual copyright protection for certain works that extends beyond the author death year + 70. This prevents swedish businesses from re-using out of copyright works on equal terms. The law does not say which these works are so there is no way of finding out until you try reusing it in Sweden.

There was a recent case where Mercedes used a since long out of copyright work by swedish author Karin Boye in their advertising. To my knowledge this is OK in all other european MS except Sweden. The Swedish law provides three semi-public organizations with legal tools to attack re-use of out-of-copyright works that they consider "threatening to the cultural heritage".

For re-users there is no way of knowing if you will be the subject of legal action until you publish your remix work. This is not fair from a legal standpoint and creates uncertainties for swedish companies that does not exist in other member states.

The value of Public Domain works has been studied elsewhere e.g. in the report Copyright and the Value of the Public Domain. These values can not be realised on equal terms in Sweden as long as this uncertain perpetual copyright protection exists.

More information

1. The section in the Swedish copyright law (1960:729) § 51: https://lagen.nu/1960:729#P51
2. Blog post (in english) about the Mercedes case: http://falkvinge.net/2014/03/18/sweden-invokes-little-known-perpetual-copyright-clause-against-car-ad/
3. News article about the legal threat that forced Mercedes to throw away an expensive advertising campaign that contained the poem: http://www.resume.se/nyheter/reklam/2014/03/19/mercedes-raderar-karin-boye-reklamen/

Ideas: 

We need harmonization of (at least) pan european copyright regulation that prevents member states from this type of unfair vague copyright extension.