YouTube cofounders Chad Hurley and Steve Chen are parting ways. The duo worked together for 15 years, starting at PayPal, then got $1.65 billion from Google. But faced a series of missteps at their incubator Avos Systems. Now Hurley is cutting his losses and focusing on just one Avos product, MixBit, and Chen is joining Google Ventures as an entrepreneur-in-residence.