Sorry about this guys, we'll get it fixed.
*explanation, if interested*
The post is actually coming back right away, but the div around the new comment is marked display:none because it was empty when the page first loaded... the javascript that loads the new comment isn't correctly clearing the display:none so you don't see it. I was debugging this for ages the other day, assuming that it wasn't coming back and that it was a server caching or data issue... but with firebug I finally noticed that it was actually right there.
*end explanation*
DCMonkey, if it doesn't come back when you F5 the whole page, then that seems like a different issue, because that has consistently worked for me.