I keep car until they have no value so I'm not affected as much (if at all)
as the frequent trader.

http://autos.yahoo.com/articles/autos_content_landing_pages/310/the-years-poores
t-performing-cars

Residual Value
Another factor that can or should be an indicator of a turkey is residual
value. John Blair, CEO of Automotive Leasing Guide, which provides
depreciation estimates for use in the automotive financing industry, says
that residual value is commonly associated with leases--as a higher residual
value typically translates to a lower monthly payment--but it's actually
more important to those who buy.

That's because leases are for a set term at a monthly payment that's set by
the bank, "but buy the car and you're stuck with it," says Blair. "It can be
quite different when you're comparing a Honda to a Hyundai."

For instance, Blair says that ALG's three-year residual on a Honda Accord is
about 55%--meaning that it is estimated to be worth about 55% of its
original value after three years--while for a Hyundai Sonata, it's only 40%,
which translates to a difference in value of $3,750 over those three years
on a sticker price of $25,000. Although Blair added that, generally
speaking, vehicles with lower residuals have lower appeal and often have
automaker incentives that apply to the purchase price, making up for some of
that difference.

What's more, the difference between vehicles can be even more pronounced
than this example. On ALG's five-star ratings system, with five-star
vehicles having the best depreciation ratings, the Accord has a four-star
rating, while the Sonata has two stars.