apt-get hang in unstable

[David Goodenough <david.goodenough@btconnect.com>]

I have an machine which I keep at unstable, and update daily.  This is mainly
so that I can keep an eye out for problems.  When I came to run apt-get today
it started quite happily, but I remembered that there was a change I had
intended to apply to /etc/apt/sources.list, so I interrupted apt-get, edited
sources.list, and restarted it.  It just hung.  So I logged off and back on
in case there was something left lying around, but that did not clear it, so
then I tried re-booting the machine and that did not clear it.  

Now no apt-get operation, except apt-get -v or -h, work.  They do not put
out any error messages, they just sit there.

Anyone got any ideas as to how to resurect it?

David