It does this old troll’s heart good to hear that folks are still getting fun out of Shields Shall be Splintered. I recently discovered that the Down In a Heap podcast discussed the rule, and that conversation was picked up by theConfessions of a Wee Tim’rous Bushi podcast, expanding the idea further in other types of armour. (I haven't listened to the whole thing yet, but it kinda-sorta sounds like a codification of Jeff's Everything Shall be Splintered idea.)
As for me, I’m still very much using it. I do limit it by using LotFP’s encumbrance
system, which makes tracking encumbrance as easy as just writing things on your equipment list. I have no problem with
hirelings carrying spare shields; shield bearer is an actual word from history. (But so far, no one has really pushed this
and I’ve not heard of it annoying anyone else at the table.)
As for who else can use it, that really depends. I swing back and forth on the players running
their PCs’ hirelings, and if the players are doing so, I let them decide when
the hireling might sacrifice a shield to protect themselves. Monsters typically do not use it, unless they
have names or the Rule of Cool suggests now is a good time for that to happen.
ADDENDUM: It appears the idea of the shield stopping some
of the damage, but not all, is a popular one.
Here’s another variation on that theme.

