The issue is not that the official unemployment rate artificially dropped this month, it is that it remained artificially too high in prior months. There are two separate data points that support this.
1) Private ADP Report
If we look at the private ADP report historically, we find quite a dispersion in month to month readings when compared to the government BLS report. But over longer periods of time, the two reports are fairly consistent. The ADP jobs report has been significantly stronger than the BLS report for a good many months, and what we saw today (and earlier in the month in terms of revisions) was some of the catch-up from the BLS. It is important to note that ADP is the largest payroll provider in the country with a very diversified mix of customers (Size, Industry, and Geography). Their survey in the US is derived from a sampling of a subset of more than 344,000 business customers that employ more than 21 million workers. Given that they provide services to large companies (more than 1000 employees), mid-size companies (50-999 employees) and small companies (1-49), they are likely to pick up employment changes very quickly!
2) Various Employment Related Economic Indicators
Over time, we typically see a positive correlation between employment, and economic statistics such as New Auto Sales and Consumer Confidence. The reasons are obvious. Those without jobs tend not to be confident and have a particularly hard time qualifying for a car loan. Both of these indicators have been rising in recent months, much more so than the tepid BLS job growth of 100,000 - 120,000 would indicate.
Romney supporters such as Jack Welch understand this. Whatever you think of his motives, he is no idiot. That is why Jack is on the record as of last night predicting the rate would be 7.9%. The problem is, Romney's entire campaign is premised on the need to make a change because the President's economic policies are not working. They have no choice but to go all birther on the BLS report, because if most americans believe the employment situation is materially improving, it is game over!