Looks like I may have finally resolved this issue. I took my X into the stealer last week, and haven't had a problem since then. Unfortunately it took them $250 in labor to diagnose the problem which turned out to be $14 worth of parts. Here's the resolution from the service department, this may be useful.

"VERIFIED CUSTOMER COMPLAINT. FOUND PROBLEM IS INTERMITTANT. CHECKED MEMORY FAULT, FOUND NO RELEVANT FAULTS. FOUND THAT WHEN ENGINE DOES NOT START THERE IS NO SPARK GOING TO ANY CYLINDER FUSES. CONNECTIONS OK, CHECKED UNLOADER RELAY, FOUND INTERMITTANT RELAY INOP. REPLACED RELAY AND TESTED MANY TIMES"

After seeing the many different suggestions, I'm guessing there is no "magic bullet" for this problem, but maybe this can help.