The amount of work that was done at the last two ISP's I worked due to being out of RFC1918 space and thus needing to do overlay networks, and all kinds of fun translating and gateways and overall making a HUGE mess of everything...

Because while there is a 10/8, once you start subnetting that and advertising it from multiple sites and start running labs that look and act like production that /8 goes quick.

Give me IPv6 any day.