The idea of a sewn love letter is metaphorically clever as you want to make those words last as long as possible and fabric is longer lasting than paper. Well, you do have the unpicker in case of mistake or heartbreak. I also like the sound of the needle piercing paper making a the irreversible hole (even if it makes a needle blunt, oops). I have experimented with the paper/thread/sewing/embroidery combo before, for example making a photo album and sewing in the photos while embroidering little bits around the photo. Cause don't you just find it annoying when the glue comes loose and they just fall out the album and in the worst case the photo gets lost? And the thread (&holes) adds lovely texture and colour.
Found this crafty solution on my friend's blog, who is based in Australia; his comment was: "saw this guy on the train today. he was traveling light in style!check out his home made suitcase / backpack solution.". Ditto, Rob, ditto.