Today is the day!
ARIN have announced today that the first applicant to ask for a block of IPv4 addresses that cannot be fulfilled has been processed, and therefore the Waiting List has been activated. You can find the official announcement here.
As of this morning (UK time), there are just 59 /23s and 437 /24s left to be allocated in the pool, a total of 142,080 addresses left. These are likely to be gone in a matter of weeks too. Returned blocks and any futher IANA distributions may be added to this pool, so may go up as well as down, but effectively today is the end of any LIR hoping to get a block of addresses larger than a /23.