We too are located in Washington State and have found that most homes built to the "NW Energy Star V 2.5" requirements meet the Federal tax credit. The exception is a ranch style house meeting the bare ES minimums - they usually have to upgrade the equipment/windows beyond ES. The requirements can be found at http://www.northwestenergystar.com/partners and look/click on the BOP1 for gas homes or BOP2 for electric homes.
We have heard differing opinions whether the tax credit will extend into 2012 - not likely though, seeing the stagnation that Congress is experiencing. They can't seem to get anything done that benefits OUR country. :(
The rebate is tied to heating/cooling energy usage. I've simulated a lot of different things trying to determine what makes the biggest impact for Atlanta - Zone 3, and equipment efficiency seems to have the biggest impact. 15 SEER with a 95% furnace (or 9.0 HSPF heat pump) usually gets a home over the hump here. If the ducts are in the attic, duct leakage makes a big impact too. CFL's also have a large impact in REMRate. I have found that it will be very hard to get there without the equipment upgrade though.
The current extension is set to expire at the end of this year. Not sure if another extension is in the works. Of course we didn't get the current one until December of last year and it covers all of 2010 and 2011. The DSIRE website (www.dsireusa.org) has a good explanation. It's under the Federal Rebates section: second one under "Corporate Tax Credit".
Hope that helps.