There appears to be a pretty good assortment of changes that could have a significant impact on the cost in your estimate.
As long as you are performing a detailed take-off that includes accurate material costs and labor units, it will be easy to account for the additional costs. However, if you are using some type of cost per square foot method, it could be a little more involved to determine the cost impact.
CARBON MONOXIDE DETECTORS. Co detectors will be required in every dwelling that has either (A) an attached garage or (B) is heated using fossil fuels. CO detectors are not required to be interconnected. The Code will also require that any time a permit is needed for existing residential work, CO detectors will need to be installed.
LIGHT BULBS. At least 50% of all light bulbs installed in new homes must be energy efficient. (CFLs or similar.)
TAMPER-PROOF RECEPTACLES REQUIRED. ALL receptacles installed will be required to be 'tamper-proof'.
ARC FAULT CIRCUIT BREAKERS. EVERY circuit in habitable portions of the dwelling must be protected by a Combination Type Arc-Fault-Circuit-Interrupter. Previously, only BEDROOMS required such protection. Now, EVERY room in the house (except for closets, hallways and storage areas...and areas required to be Ground-Fault protected like garages, bathrooms, kitchens and basements) will require an AFCI at the panel.
INCREASED COVERAGE FOR GFCI. GFCI protection will increase to include ALL basement receptacles and ALL garage receptacles. EXCEPTION: Circuits protecting burglar and fire alarms.
FIRE SPRINKLERS. Last and certainly not least is the requirement that ALL townhouse constructed under the 2009 Code have fire sprinkler systems installed in compliance with NFPA13D after January 1, 2010. Single and Two-family dwellings will be required to have fire sprinkler systems beginning January 1, 2011.
The 2009 IRC references the 2008 National Electric Code. It is within the 2008NEC that the requirements for AFCIs and tamper proof receptacles are found.
The 2006 IRC is still referencing the 2005 version of the National Electric Code which is why these electrical updates will only appear in January for those that adopt the 2009 IRC.
Some states only use the current version (2008) of the National Electric Code for residential wiring, which is why some states are already implementing tamper proof receptacles and AFCI breakers for all locations.