Trek has been steadily downgrading their bikes, in general, so a 2008 is superior to a 2009, to a 2010.
In the 2.3 series, in 2010, they eliminated the carbon stays (because it rode like a $2000 MORE expensive bike)
and made if full 105 instead of using a Botranger crankset. Not an improvement to most.
Most people think the 2009 is the best 2.3 ever. And they are on sale NOW.