Failures trying to add a package:

gzip: (stdin): unexpected end of file
tar: end of archive volume1 reached
tar: unexpected EOF on archive file
pkg_add: [...failed...]

Redownloading didn't help, and they open on OS X, so I really don't 
think it's a problem with the package files.

Same error trying with the packages located on a flashdisk or local 
partition. I can't try adding through FTP as I have no modem or airport 
card at the moment.