Every now and again, after clicking Preview or Submit, I'll get an error like this:
SQL ERROR [ mysqli ]
Lost connection to MySQL server at 'reading authorization packet', system error: 0 
An sql error occurred while fetching this page. Please contact an administrator if this problem persists.
Usually clicking Refresh (or back / Submit) fixes it, so it's not a huge deal. I've just seen it a half-dozen times in the past week, so I thought I'd bring it up.
I would at least change to a custom error page though, so programmers like me don't go, "oooo mysqli driver!" and start thinking about injection attacks.
This error usually means some kind of network or connectivity issue (for us it was related to persistent apache connections), if that helps. Usually there's more useful info in mysqld.log