POC (Proof of Concept) Before approaching VCs ?

Dearest Entrepreneurs of YC,

Methinks I have a great idea for a Web startup; since I have never really plunged into the whole VC scene ever before, I was wondering should I have a Proof-of-Concept BEFORE I approach VCs ? Thing is, the POC might set me back by a few months, where I could be devoting on all aspects (marketing, funding, ideas, recruitment).