Good news!
This case is about a Star Wars Lego collector. But I think the outcome means we (MLP collectors) will have a good chance to claim and be reimbursed too if the customs open a mib pony.
link (all in swedish, I haven't found anything about this available in english yet...):
http://hallandsposten.se/nyheter/halmstad/1.1901622-legosamlare-far-ratt-mot-tullverketWhat it says:
In September 2012 the swedish customs opened a package, for legitimate reasons, but this caused the mib item inside to be slit open. Item was a htf collectible Star Wars lego ship.
The buyer, from Halmstad, claimed the value came down from 1 838 SEK to about 1 000 SEK.
The customs have now agreed to reimburse him with the difference, 838 SEK (about $130 USD).
There is a reference to a specific part of swedish law as well, I'm not sure how to translate it though...
Swe people, bookmark the article
so you know what/how to claim successfully if it happens to you.