Some ideas and thought about posting:

• Standardize! Sometimes experience shows before hitting "Submit", sometimes after. Some places show you your post, as it appears on the page, after you post, some only show the TEXTAREA box.
• Have a link to instructions (or put them below the TEXTAREA box, with a note to look below) These should explain everything about posting, especially how to do CODE, < vs. &lt;, linking and how to create actual [non-linking brackets], etc.
• Have some error checking to eliminate empty posts, even something as simple as just checking for a 0 length post
• Allow posting as "Anonymous Monk" when you are logged in, if so desired.
• Make the TEXTAREA box bigger! Perhaps have it go full-screen, then start the table with the boxes on the right.
• Have intelligent parsing of brackets - perhaps a common escape code like an asterick as the first thing after an open bracket indicates that it is NOT a link.
• Allow a way to link to specific nodes by number!
• Explain what that "position" field is that sometimes appears below the "title"
• Allows other places to do the automatic line numbering, like Craft does.
• Detect people who did not use the CODE tags automatically, perhaps by flagging lines...well, ok this would be very complicated. But still possible.
• Warn users who have very long lines that cause my browser to create a very large and annoying window. :)
• Make the TITLE box larger (hrmm..looks like it does not even have a size now. Sizing it larger (like perhaps 40) should be safe, as the TEXTAREA below it is set to 60 (which should be larger too - see above)
• Allow a standard "sig" to appear in the TEXTAREA box for those that use them in every post