Both bugs sound pretty serious.

Unpatched Mac bug gives attackers “super user” status by going back in time.

This vulnerability can allow an attacker root access to OS X.  Time related bugs like this sudo bug are really difficult to notice, but at least it’s fairly difficult to trigger.

Rendering bug crashes OS X, iOS apps with string of Arabic characters (Updated).

This bug, on the other hand, is likely to cause all sorts of issues as it becomes more well known.  Any application that uses Apple’s CoreText  will crash if it sees a certain string of Arabic characters.  There aren’t currently any security implications, and I admittedly thought of sending the text to Mac-using friends.  However, if your browser crashes every time you view a certain site or text message, this is why.  For some reason, this bug reminds me of the ping of death (e.g., in early versions of Windows).