This is the third in two months and includes a new feature enabling consoles to serve as receiver units for Sony's LocationFree TV. First seen last month, LocationFree TV includes a base station which broadcasts the signal from one television set over a wireless broadband Internet connection.
The Sony PSP v. 2.5 firmware upgrade uses the console's existing wireless broadband receiver to make the device a LocationFree TV as well.
The upgrade also fixes some minor bugs to the Web browser, and allows internal clocks to sync with Internet-based time servers.
Perhaps one of the main reasons that Sony is releasing the firmware is that it will close some doors that homebrew hackers have opened in the machines that allows them to run non-licensed code. Sony doesn't like that sort of thing.
More at MacWorld, here.