At work (a larger enterprise in Europe) we already see quite a bit of pain with IPv4. B2B connections are increasingly not using globally unique addressing anymore, so we often need to use prefix NAT and application level proxies to bridge clashing address space. This in turn is a support nightmare and is hurting reliability.
Our network guys seems to love the extra complexity, though.
I hate VPN-ing into other people's networks, it is such a pain-point. As you say, you have address/space clashes, and all kinds of other (sometimes even security) problems.
It sounds easier than it is, the main issue is scaling. Need to connect to one other person for B2B? Trivial. Two? A little harder. Ten, twenty, fifty, ouch...
Our network guys seems to love the extra complexity, though.