This means that all petitions beyond the cut-off date will be frozen until all pending petitions are processed and new visa numbers are appropriated.
The visa bulletin, released a few days ago, summarized the availability of immigrant numbers during August. Section F of the bulletin carried the following information:
A total of 50,000 numbers were provided for use in the Schedule A (EX) visa category which was established last May 2005. Visa demand in this category is approaching that limit, and may require the establishment of a cut-off date as early as October. Once all 50,000 numbers have been made available under the current limitation, processing under this category will end.
Source: US State Department Visa Bulletin