Oh my God, I know exactly what you mean. I've given up and decided to just guess if there is such a question on the test. I've actually done this with a few other topics (anti-arrythmics for sure).
I know so many people who spent an entire afternoon going over some stupid topic that less than .1% of MD's have ever encountered, just to find out that there wasn't a single question on the test or there was and they got it wrong anyway.
It's a surprisingly liberating feeling to just accept defeat (or apathy), and I doubt it will affect my score (I'm not shooting for a 260 like most people who post on this board).
Nonetheless, if somebody has a magic mnemonic I appreciate it.