Wait, does your school REQUIRE step 2 by December or HIGHLY RECOMMEND step 2 by December? I only ask because our school highly recommends that we take Step 2 by December 1st (they think we're stupid and will fall for this trick so that they can see our scores before rank lists are due). However, the absolute rule at our school is that we must take Step 2 by Feb. 1st.
Anyways, if you are required to take step 2 by December, I guess you should take it as late as possible but within your school's deadline. Definitely don't send them automatically and don't even send them, especially if disaster strikes. Amy is right. Most programs and specialties don't REQUIRE step 2. But competitive residencies may use step 2 as a discriminating factor when deciding between two strong candidates. But if you're like me and not applying to a competitive field, screw step 2. You don't need it and neither do they. And if a program "requires" step 2 before ROL entry time, tell them to piss off cuz most of your other programs won't require step 2 prior to Feb. 23rd.