I was just peeking at the A's roster. Right now, I figure there are 23 spots on the A's roster that are pretty secure:

Pitchers (10):
Zito, Harden, Haren, Blanton, Dotel, Cruz, Calero, Rincon, Duchscherer, Yabu.

Catchers (2):
Kendall, Melhuse.

Infielders (6):
Hatteberg, Ellis, Ginter, Crosby, Chavez, Durazo

Outfielders (5):
Byrnes, Kielty, Kotsay, Swisher, Thomas

 
Yabu's role isn't clear, but I'm figuring the A's didn't spend $1M on him to have him pitch in AAA. Which leaves:

On the bubble (2 slots, 7 players):
Meyer, Etherton, Street, Saarloos, Tyler Johnson, Scutaro, Dan Johnson

Which two of these seven make the team depends on two decisions: who the fifth starter is, and whether they'll use 11 or 12 pitchers.

Assuming there will be 11 pitchers:

There are four guys battling for the fifth rotation spot: Yabu, Etherton, Saarloos, and Meyer. Meyer was "Plan A", but he has struggled this spring, and may get some more seasoning in Sacramento. Saarloos is coming back from injury, and will probably end up in AAA to build his arm strength some more.

So starter #5 is likely either Yabu or Etherton. If it's Yabu, Huston Street probably makes the team in the bullpen. If it's Seth Etherton, Street probably goes to Sacramento, and Yabu ends up in the pen.

Rule 5-er Tyler Johnson hasn't pitched well, and is likely now to be offered back to St. Louis. He has an outside chance if the A's decide on 12 pitchers, I suppose. But really, he doesn't deserve to be on the team ahead of Street or Etherton.

My guess is that Etherton will be the fifth starter, Yabu ends up in the pen, Street, Meyer and Dan Johnson get a little more time in AAA, Tyler Johnson is sent back to St. Louis, and Marco Scutaro ends up with the last roster spot.