I sent my Mezuza to be checked by an expert sofer and the first thing he pointed out to me concerns the Tagim of the Shaatnez Getz letters. He told me that the Tag on the right should be higher that the Tag on the left, something I never heard before. In the picture below you can see that in my Shin, the taguim in the left and in the right are as tall - according to this Minhag, the one in the right should be higher.
This expert sofer noted that today many Rabbis require the sofrim to write all Tagim like this, much like the widespread Minhag of making the right-hand Tag of the Lamed higher than the left-side Tag (see pic in the right).
But what's the reason?
According to the Kaballa, the right symbolizes Chesed, kindness, while the left symbolizes Gevurah, austerity, and this concept is often times mentioned by Chassidic Rebbes. That's the same underlying reason why the strings of the Tefillin Shel Rosh should be longer on the right side than in the left side - we always try to ensure that Chesed is in more evidence.
Not long ago, a Chassidic Rabbi was in my parents house and they asked him for a Bracha for Parnassa. The Rebbe asked them to check if the Mezuzas of the house had the right-hand Tagim higher than the left-side ones, since Parnassa is connected to Chesed and therefore having the high right Tag is a Bracha for Parnasa.
I often times do a "rainbow" Tag (see below) when two or three Shaatnez Getz letters appear together, but it seems that I will have to stop it if I am to comply with this Minhag - in the rainbow Tag the Tag of the right is the smallest.