In all of the cases so far (that I've checked) it seems that the registrar of the domain has been based in the US. So to seize a domain it would be sufficient to do this at the registrar level, instead of the registry level.
If the domain has been sized via the US-based registrar it's nothing to worry about.
If - on the other hand - the domain has been sized at the registry level (and the same would have happened with another foreign registrar) this would be one large reason for me to use other TLDs in the future. However, if this is really the case it makes me wonder why piratebay.org hasn't been sized yet (this domain is registered at a German registrar).
If the domain has been sized via the US-based registrar it's nothing to worry about.
If - on the other hand - the domain has been sized at the registry level (and the same would have happened with another foreign registrar) this would be one large reason for me to use other TLDs in the future. However, if this is really the case it makes me wonder why piratebay.org hasn't been sized yet (this domain is registered at a German registrar).