Today, we learn what they're doing with some of that depth. From the Colorado Rockies' official Twitter feed:
#Rockies acquire RHP Guillermo Moscoso & LHP Josh Outman from Oakland in exchange for OF Seth Smith.
Smith is 29 and has been a more-or-less regular outfielder for the Rockies the last three seasons, posting a career triple-slash of .275/.348/.485 and a 110 OPS+. That's pretty good, but as for many Colorado hitters, it's skewed by Coors Field (.925 OPS at home, .750 on the road), so it's anyone's guess how he'll do in the Oakland Mausoleum. Just yesterday, the Rockies signed Smith to a one-year, $2.4 million contract, avoiding arbitration.
In exchange, the Rockies get a couple of pitchers who should compete for their rotation, lefthander Josh Outman (career 114 ERA+) and Guillermo Moscoso (120 ERA+ in his one full year in the Oakland rotation in 2011).
The Rockies' starting pitcher depth chart is pretty thin and includes several pitchers with minimal major league experience (Drew Pomeranz, Tyler Chatwood and Alex White), so this should create some competition during spring training.
It's not a big trade, but does involve three major league players who were a little above league average and could help both teams. You don't see those work out too often; this one just might.