Good question.  I added a (slightly rough) analysis of that question to the post.  Looks like there's no sign whatsoever of improving fuel economy through the end of last year, at least.
A late addition to this thread: Lou Grinzo has the latest figures on gasoline consumption from January:

http://www.grinzo.com/energy/blog_entry_archive/2006/03/2006x03x29_5.html

It says that U.S. January gasoline consumption dropped 0.6% from a year ago. In conjuntion with Stuart's report that miles travelled was up 3.8% from a year ago, that points to about a 4.4% increase in MPG, which would be substantial.

Of course all these figures have a fair amount of uncertainty, and given Stuart's analysis showing no trend in increasing MPG throughout 2005, this sudden increase in January is rather suspicious. It will be very interesting to see if it carries on into February.

Well if I'm reading the chart correctly, this makes sense.

IN SS's MPG chart, it appears MPG is up almost 1 MPG, which would equal close to 4.4%.

Am I reading it right?