I'd like to point you to USS Mariner's reaction to the trade of Clement for Wilson. They do an excellent job summarizing the pieces of the deal, and their conclusion is (from a Mariners' fan's perspective):
For two guys with minimal value, the Mariners parted with five young players...Pittsburgh is the easy winner of this deal, as they get some interesting young talent and shed some salary without losing much that will hurt them. The Mariners could still salvage this by moving Wilson before Friday’s deadline for a younger SS with more long term potential, but if they stand pat with Wilson as the team’s shortstop for 2009 and maybe 2010, color me disappointed.
Click through for more advanced analysis, its worth a read.