Having tried to recreate the index, after four hours this process has crashed too.
/usr/lib/ruby/gems/1.8/gems/lockfile-1.4.3/lib/lockfile.rb:364:in `unlock': /home/fred/.sup/lock (Lockfile::StolenLockError)
from /usr/lib/ruby/gems/1.8/gems/sup-0.12/lib/sup/index.rb:87:in `unlock'
from /usr/lib/ruby/gems/1.8/gems/sup-0.12/bin/sup-sync:206
from /usr/bin/sup-sync:19:in `load'
from /usr/bin/sup-sync:19
That's it for me I think. Maybe I'll try Sup again after it's been through a few more versions.