As moderators, we occasionally need to deal with users who have needed intervention of some sort and don't warrant a suspension, but need to be monitored so we can follow up if they continue to cause problems. There is currently no way for us to automatically be informed of their activity. It would be nice if a "watch list" of sorts could be added to the moderator tools. We already have annotations, but this only allows us to see who has been moderated, not what they've done since.
One way this could be implemented is if under each user who has been recently annotated, you could click to expand and show their recent activity - last login, questions asked, edits/deletions, etc. This would would automatically make relevant info readily available for users who have already been annotated, making checking up on recent offenders a simple task. Alternatively, there could be a separate Watch List section on that page, with the same concept of clicking to expand a user's activity, but users would be specifically added to the watch list.
Based on conversations with other moderators and my own experience (for reference, I moderate on SU), I believe this would be a very useful feature for keeping tabs on borderline users.