Here's a recursive one at 86. Hate the data structure BTW!

use Data::Dumper;

my $h = f(qw[ foo => zoo moo too
              bar => car far
              bar => zar tar
              qux => mux ]);


print Dumper $h;

sub f {
  $_='';my@v;{$_&&push@v,$_;$_=pop;redo until/=>/}
  $k=pop;$h{$k}=[@v,@{$h{$k}}];@_?&f:\%h
}
[download]

79 chars

sub f {
  $_=my@v;{$_&&push@v,$_;$_=pop;/=>/||redo}
  $k=pop;$h{$k}=[@v,@{$h{$k}}];@_?&f:\%h
}
[download]

75 chars

sub f {
  my@v;{$_=pop;/=>/||(push@v,$_)&&redo}
  $k=pop;$h{$k}=[@v,@{$h{$k}}];@_?&f:\%h
}
[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print