What steps will reproduce the problem?
I don't know exactly when it started

What is the expected output? What do you see instead?
When I run git annex unused I get

    unused . (checking for unused data...) (checking master...) git-annex: Cannot decode byte '\xb4': Data.Text.Encoding.decodeUtf8: Invalid UTF-8 stream

Most likely I have added some file with a strange encoding that git-annex can't decode. The problem is that the unused process aborts because of this.

What version of git-annex are you using? On what operating system?
 3.20120522, Debian testing

> I've just fixed this bug in git, will be in the next release. --[[Joey]]
> [[done]]