How to automatically set PDF 'Activity Subject' from template subject?
Tracked this one down. It worked out of the box in 4.4.x, but doesn't in 4.5.x. Not sure whether it was deliberate, but it's pretty easy to 'fix'.

Edit templates/CRM/Mailing/Form/InsertTokens.tpl and change:

  cj.post( dataUrl, {tid: val}, function( data ) {
    if ( !isPDF ) {
      if (prefix == "SMS") {
          text_message = "sms_text_message";
      }
      else {
        cj("#subject").val( data.subject );
      }


to:

  cj.post( dataUrl, {tid: val}, function( data ) {
    cj("#subject").val( data.subject );
    if ( !isPDF ) {
      if (prefix == "SMS") {
          text_message = "sms_text_message";
      }


It's explicitly only setting the Activity Subject for non-PDFs, which is weird. It looks like it was accidentally(?) reverted when SMS support for recurring contributions was being added. Have created an issue.