Ability to preview private messages and chatter box messages. It is very scary to post a message for the first or second time in your life and not be able to see how others might see it.

I often post on my Private scratchpad, which allows me to preview again and again, prior to posting anywhere (inlcuding /msg and CB). Every monk's home node has a Private scratchpad which other monks can not view. Granted that there are some differences between /msg, CB and other posts (such as length), but this should be pretty much WYSIWYG. Obviously, this is not as convenient as the ability to preview on /msg or CB, but it is an alternative.

Of course, this also applies to previewing updates.