According to the USPTO website, there are new series codes for utility/plant and provisional application serial numbers. The new codes are "12" for utility/plant applications and "61" for provisional applications. The first applications of 2008 were 12/5,841 and 61/9,389, so the new series must have been implemented in December 2007.
In a related development, the USPTO has implemented a new electronic filing system for reexamination proceedings. Reexamination request filed electronically are assigned control numbers starting at 10,000 for inter partes and 1,000 for ex parte requests. Paper filings will continue to receive numbers in the normal sequence. The series codes for ex parte and inter partes reexaminations are 90 and 95, respectively.