Japanese computer site Akiba warns users that the first batch of Intel Pentium D 900 series processors that have arrived in Japan may not have Enhanced HALT State and Enhanced Intel SpeedStep Technology (EIST) enabled.
Because some power-saving features aren't fully functional power consumption on these processors may be 10W to 15W higher than normal.
Akiba goes on to highlight a footnote to the Intel Pentium® D Processor 900 sequence and Intel Pentium® Processor Extreme Edition 955 datasheet and specification update stating that Enhanced HALT State and EIST will be functional for specified units of these processors through a BIOS update which is expected some time in the second quarter of this year.
Additionally, according to Intel's latest errata there is a possibility that during an Enhanced HALT or EIST ratio transition the system may hang. More info at The Tech Report.