As found here: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=350210 the current version of unshield will not extract files due to a checksum error on AMD64. I made a patch from that bug report, but I'm not sure if it's good enough to put in portage as-is (see other bug report for details). Hopefully someone else can fix up the ebuild and possibly the unsigned long int vs. unsigned int vs. uint32_t detail for portability.
Created attachment 98177 [details, diff] md5 patch for amd64
AMD64, it would be nice if you were to fix this, as the current version is ~amd64 but broken.
fixed in cvs, thanks for the patch