In sqldeveloper 1.5, if you don't want to have the option of saving the password for a connection try this:

Edit the sqldeveloper/bin/sqldeveloper.conf and add this:

AddVMOption -Dsqldev.savepasswd=false

Adding this will remove the checkbox to have the ability to save the password. I added this a while back and forgot until a recent post on the forums reminded me. A customer needed to for some complicity they had to meet.