I'm looking at one of my picks right now....it's virtually flat across the bottom and each side has distinct "chamfered" wear on it, probably due to using this one a fair bit for tremelo picking on the octave mando (I tend to turn the plectrum slightly to one side when I do that, rather than using it right on the point...probably bad technique but I seem to get a smoother tremelo that way).

I reckon this one's for the bin now!

I mostly use Jim Dunlop Turtle plectrums and generally find that once the dye had completely worn off the logo they're less useful for more precise work, so they get relegated to strumming for a while before being discarded.

OTOH, I have a friend who seems to be able to play very precisely even with picks worn more than this one that I'm about to discard.

So how often do you replace your plectrums (through wear rather than losing them....that's another story)?