I remembering hearing a p'shat in the name of the Gra about Yom Tov, that I would really love to know the source for. I am not normally one for Gematriyos but the genius of the Vilna Gaon is quite something!
We know from the Gemarah in Beitzah 15b that the avoda of Yom Tov is to split it 'חצי לה (half for Hashem - i.e. to engage in spiritual pursuits) and חצי לכם (half for yourself i.e. to enjoy the physical side that Yom Tov brings).
The Vilna Gaon states that this is hinted to in the very words 'יום טוב' - 'Yom Tov'
The first part of our service of the day is 'חצי לה, so if you work out the gematriah of 'לה you have ל which equals 30 and Hashem (spelt YHVH) which total 26. Together this makes 56. Since it is HALF for Hashem, you halve 56 which gives you 28.
The second part is חצי לכם. The gematriah of לכם is 90 (30+20+40) and half of it is 45.
So when you combine these two halves you get 28 + 45 = 73, which is the very same gematriah as יום טוב (i.e. 10+6+40+9+6+2 = 73)