IMO it is cleaner to use $1 & $2:

my (%foos, %bars);
while( my $line = <DATA> ) {
  chomp $line;
  if ( $line =~ /^foo ([^:]*):([^:]*)$/ ) {
    push( @{ $foos{ $1 } }, $2 );
  } elsif ( $line =~ /^bar ([^:]*):([^:]*)$/ ) {
    push( @{ $bars{ $1 } }, $2 );
  } else {
#    warn qq( "$line" is the wrong format.\n );
  }
}
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Or named captures if you're using 5.10:

my (%foos, %bars);
while( my $line = <DATA> ) {
  chomp $line;
  if ( line =~ /^foo (?<KEY>[^:]*):(?<VAL>[^:]*)$/ ) {
    push( @{ $foos{ $+{KEY} } }, $+{VAL} );
  } elsif ( $line =~ /^bar (?<KEY>[^:]*):(?<VAL>[^:]*)$/ ) {
    push( @{ $bars{ $+{KEY} } }, $+{VAL} );
  } else {
#    warn qq( "$line" is the wrong format.\n );
  }
}
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