us.aminet.net is the 'core' of Aminet - all uploads get forwarded to that server and are processed there.
The hard disk(s) of that server died back in August. The server admins (washington university personnel) tried to reupload as much Aminet stuff as possible, and the archive seems to be back again.
The problem is, that uploads still do not work. You can FTP into the uploads directory of your local Aminet mirror and you'll see lots of unprocessed uploads. The WU guys probably missed (or messed up) some of the scripts responsible for dealing with uploads when installing the backups.
Urban Mueller (Aminet admin) doesn't respond to e-mails, and he's probably the only one who could do something about it.
Conclusion: Aminet works, but it doesn't accept uploads right now.