If I have a 3750 stack, and I configure layer 3:
interface vlan 10
ip address 10.10.10.1 255.255.255.0
What happens if my primary switch fails?(which is where I assume those L3 definitions exist. I can comprehend the loss of ports/L2 when a switch fails but the layer three definiations...do they move to another switch of the stack?
The config is shared among the members of the statck. If the primary switch (stack master) fails some other switch takes over as primary (master) and the layer 3 definitions are maintained in the new primary (master). That is one of the advantages of the stack concept.