There have been those to suggest the Philadelphia Union's addition of Freddy Adu is essentially a swap for Carlos Ruiz. While the timing of the two moves makes such a statement tempting, the reality is that the two players fill significantly different roles.
Ruiz was very much a forward, and one who was particularly focused on putting the ball in the back of the net. Adu is is a player whose best attributes are his ability to break down a defense and set up teammates.
The Brotherly Game, SB Nation's Union blog, recognizes this and outlines the various ways that Peter Nowak may choose to deploy his newest weapon:
The first of these options would, essentially, be a continuation of how the Union have played up to now: two strikers up top, two central midfielders, and two wingers. Adu would be the more advanced central midfielder, and he would be backed up by the more defensive Brian Carroll. Nowak would be left with several options at striker; Jack McInerney, Veljko Panouvic, Sebastien Le Toux, or Danny Mwanga could start as forwards, while Justin Mapp and Keon Daniel could take up the wing positions. Le Toux could drop back to winger as well, sending Daniel to the bench.
The other possible way that Adu could be used is as what could theoretically be used would be as more of a withdrawn forward in a formation that would play very much like a 4-5-1. The biggest downside to this formation would be forcing Sebastian Le Toux back into the midfield, where he's be significantly less effective.