This is actually a very real temptation for us because we have an old '89 GMC van that would qualify (17 MPG Highway) and we've been constantly dumping money into it to keep it running.
Cash for Clunkers Car Buying Stimulus Bill- Yahoo! Autos Article Page
The sad thing is, the cars turned in get scrapped and are not to resold as used vehicles. We've had the van since our son was born - bought it to replace the Ford Tempo that was then too cramped to accomodate two children's car seats plus two adults comfortably on long trips - and it therefore holds some sentimental value to us, going back to when our kids were still little. But, we'll have to give it some serious consideration as to whether to let sentiments over it keep us from taking advantage of having $3500 to $4500 to put towards a replacement vehicle.