As Victar proposed: (somewhat modified)
(1) better notification of locked fields and profiles for curators, and (2) showing locked fields or profiles by (of) other curators.
For issue one(1): (a) I'd like to see lock icons on tree view nodes of fully-locked profiles (whole profile lock) and (b) show an icon on locked fields in the merge panel. It would also be great if the curator could add "lock notes" to individual fields that could be displayed in a mouse-over.
I don't think issue two(2) will ever go away, but most accidental instances can be deterred by displaying a warning when you try to unlock a field locked by another curator: it could read something like, "This field has been locked by <name>. Are you sure you wish to unlock it?" A similar message could appear when you are about to take over curatorship of a profile, to serve as a reminder.