How much say do you have in office location?

[SoCalBruin]

When and how does office assignment work during the hiring process?

Do you they offer you X office, take it or leave it?
Do you give them a preference during an interview?
When does transferring become a viable option?

I ultimately want to end up back in CA, but I realize that NYC might lend itself more opportunities starting out.

[craven]

You generally interview specifically for the office, not just for the firm.  This is a little more flexible in OCI, where they may send one attny for the entire firm.  Once you head back for callbacks though, you're locked into that particular office. 

If they're doing OCI for NYC and you want to go to LA, profess interest in LA to your OCI interviewer.

[SoCalBruin]

If you apply specifically to an office, is it possible to apply to multiple offices within the same firm?  Or is this ridiculous?

[craven]

You can do it, but in areas where they're particular about your desire to move to their market, it doesn't bode well.