I personally like the Rune when my team has a lot of Auto-attackers, makes fights a bit easier when everyone is sustaining on targets I slow/CC.
Anyone else?
The secret to font of life is to pair it up with the Unholy Grail and the Ardent Censer.
There are some runes never used because they are put on the same line as better options........which is why they made the change and put magical footwear and stopwatch on the same line because they worked great together and saved you a chunk of gold you would have to spend.
I take it on some of my HP heavy junglers. Makes it a little easier to keep your laner in the fight when you can show up with a red buff.
Font of Life actually makes 
support viable so I usually take it on her.
Supports
It's a bad rune generally. For one, it only makes sense to take bottom lane. How often do you have access to any form of CC as Janna, for example? Once with your W and another time with your Q. So, if your ADC is smart enough to autoattack the enemy you W, then it can grant 11 HP at level 1, which is ok, but then, at something like level 10, it only grants 15. The fact that it's very situation early game and very weak later makes it very unreliable. Instead, Bone plating is so much better, because it will block quite a lot of damage. Demolish is also bad.
if anyone uses Font of life anymore, its Trundle. And that's about it.
I play 
support as my main and I always build with it (that and revitalize), since glitterlance pretty well keeps it in effect most of the time on the opposition.
boneplating is just too broken to pass up for font of life sadly
I take it on enchanters like Janna, Lulu, and Soraka.
:^)
