I will modify two of my previous suggestions.
1. Private message
Show in Outbox which of private messages were read by recipients.
No please. This will be used as a tool to pester people. Removes privacy and unnecessary. Just check when they last logged in.
: Add checkbox "Notify the sender that you have read the message." The recipient can click it at will.
I suppose, Bitcointalk employees could use this option as well because they're receiving a lot of messages from different members every day.
And the recipient's last login date, in many cases, don't say anything to the sender whether the message has been read or not.
2. Banned accounts
It seems like theymos is likely even against showing which users are banned publicly (not sure why, especially when people are reporting dozens of users a day that are already permabanned and it's time-wasting for both users and staff to have to report and handle these).
If theymos is against of showing which accounts are banned, then maybe he make an exception for members that have 300 good reports at least? This will reduce an extra work for active reporters and moderators.
: Show the 'Banned' marks to the members which have more than 1000 good reports.
I believe that reporters with such statistic are not so many but with this implementation their effectiveness will significantly raise.