"sid" doesn't always equal "unstable":

[jidanni@jidanni.org]

See, "sid" doesn't always equal "unstable":
$ apt-cache policy ffmpeg
ffmpeg:
  Installed: 5:0.6~svn20100603-0.0
  Candidate: 5:0.6~svn20100603-0.0
  Version table:
 *** 5:0.6~svn20100603-0.0 0
        500 http://ftp.tw.debian.org sid/main Packages
        100 /var/lib/dpkg/status
     4:0.6-2 0
          1 http://ftp.tw.debian.org experimental/main Packages
     4:0.5.2-1 0
        500 http://ftp.tw.debian.org unstable/main Packages
Due to my
# cat /etc/apt/sources.list
deb http://ftp.tw.debian.org/debian-multimedia sid main
deb http://ftp.tw.debian.org/debian experimental main contrib non-free
deb http://ftp.tw.debian.org/debian unstable main contrib non-free