Here's a look at who has the most appearances, and in what role.
3-1 over LA Galaxy
2-0 over Shandong Leueng
6-1 over Ventura Fusion
vs. Earthquakes

Some of these are pending some clarification. Sounders FC staff got back to me with some adjustments. Ok, it was Matt, but he is staff.

Keepers
Keller - 2
Eylander - 3
Dragovan - 1
Guppy -1

Defenders

Sturgis - 2 LB, RB
Wahl - 3 CB
Graham - 3 CB
Riley - 3 RB
Scott - 2 LB
Jackson - 2 CB
Danso - 2 CB
Brown - RWB, 2 LWB
West - LB
Schmid - CB
Ianni - 2 CB
Kirk - RB

Midfielders
Zakuani - 3 LW
Evans - 3 CM
Alonso - 3 CDM
Le Toux - 2 RW, St
Screpis - CM, CM
O'Brien - 2 CAM
Caugherty - CM, RWB
Nyassi - 2 RW
Neagle - LM, RM
King - 3 CM
George - LM, RM

Forwards
Montero - 3 St
Jaqua - 3 TF
Pore - 2 St, RW
Levesque - TF, RM, CM
Olivereira - St
Clark - 2 St

Five players had changes

I have only included those that started halves, as late substitutions in the second half of these exhibitions don't seem to indicate much. For the role of appearance I have tried to compile based on the game reports from Matt Gaschk so as they are as consistent as possible. Sounders FC have used a straight 4-4-2 [[:, and a 4-4-1-1 [[-- so far. They have not used a Holding or Defensive Mid yet, at least according to the live blogs.

Legend
WB - WingBack, a defensive player on the sides that will make relatively frequent overlapping runs &/or crosses the ball into scoring positions
CAM - A central attacking midfielder. Someone who is tempo and pace of the offense and steers the movement of the team through his position and passing
St - Striker, I am using this as a central offensive forward who plays with ball at the feet. This can include a second striker such as Landon Donovan in a 4-4-1-1.
TF - Target Forward, a head player who tends to be the target of big crosses and corners. For American fans think Brian McBride or Brian Ching.
CDM- Central Defense Midfielder, also known as a Holding Midfielder.

Just updated with game 4 in Cali. Looks like they started the probably starting lineup minus Ljungberg who would replace one of Evans or Le Toux. Nyassi didn't start the final Cali match.