I've written several times about the inexorable decline in available IPv4 space and why that means we're all going to have to get our heads out of the sand and learn IPv6. If you read that particular piece -- written more than two years ago -- you'll recall that I opined that it'd only be a couple years before we'd all be forced to learn IPv6. Of course, that hasn't come to pass. ARIN (American Registry for Internet Numbers) still has more than two /8 IPv4 blocks (each with more than 16.7 million addresses) of space available to be allocated, and there's undoubtedly still a lot of slack space in the allocations that have already been made to ISPs. So things have not reached the crisis level that I imagined they might two years ago.
That said, North American ISPs are starting to tighten their belts with IPv4 allocations as they see the later phases of ARIN's IPv4 Countdown Plan near. As that happens, it will become increasingly difficult for ISPs get IP space from ARIN, and so it will be more difficult for downstream organizations to get space from the ISPs. So even though we might not actually ever be "out" of IPv4 address space, its scarcity will have far-reaching consequences.
One recent example I ran across was Northeastern U.S. ILEC FairPoint's use of /31 network blocks for handoffs to business DSL customers. Their use was obviously an attempt to reduce the consumption of address space, because these blocks are incompatible with a large swath of customer premise equipment (typically, only real routers know how to use these tiny two address subnets, which lack a network and broadcast address found in the more typical /30 block). Make no mistake: The early effects of aggressive address space conservation are already being felt and will only get worse.