It's bad news because the Mets also signed Moises Alou, who was one of only two players (Andy Pettitte is the other) ranked higher than Zito (according to Scout.com) in the free agent rankings. This means that if Zito signs with the Mets, the A's would only get the Mets' second-round pick, not their first round pick. The Giants will get the Mets' first-rounder.
To increase the A's odds of getting a first round pick from Zito, we have to root for Tom Glavine to stay with the Mets, which would make the Mets less interested in spending money on Zito. Then we can root for Zito to sign with someone like San Diego, which would put Zito in the other league, and net the A's the 23rd pick in the draft.
Zito recently met with the Texas Rangers. I wouldn't really want to see Zito in the AL West, but the Rangers have the 16th pick, which is the highest possible pick the A's could get for Zito. So at least there's that.
Update: Glavine re-signed with the Mets, but according to Ken Rosenthal, the Mets are still going to go after Zito. Boo.