The nationwide credit is new. Here in Washington state, we've been able to deduct sales tax in some past years only as a consolation prize for having no state income tax to deduct. And it doesn't happen every year.
You're right. No sales tax if bought before the end of this year. I looked it up on the IRS page, but can't post the link due to not having 5 posts yet.
The federal tax deduction for sales tax has been available every year since 2005 and is set to expire in 2010 (unless otherwise extended by Congress). The only difference this special auto sales tax deduction provides is it allows people who don't itemize to take it as an above the line deduction as well as individuals who do itemize and live in a state with income tax to deduct both income tax paid and auto sales tax paid (assuming this is larger than sales + auto tax paid). It doesn't make any difference for people who itemize and live in a state with no income tax, as they're eligible to take the sales tax deduction anyway and can't "double dip" and deduct the auto portion twice.
Unfortunately, I was there for 3 hours, way longer than I wanted to wait .. my test drive took more than 1/2 hour going over 30 miles of up and down hills, etc.