If I have a 1/1 no +1/1 counters on it and then I activate {Thrown of Geth} and sac {Arcbound Worker}, can I place the modular counter on the 1/1 and then proliferate that counter with the Geth?
Sure! The {Arcbound Worker}s ability will go on the stack after the proliferate effect, and will resolve first. By the time you proliferate, your +1/+1 counter will be ready to go!
RESOLVED