memo is just memo, it works for many people, but it is not the law (even with law, they can always find way to get around with it ), there is alwasy some exception. Yes, a few people come to us for WOM, and some still wait, some got card soon after the WOM. many of them should be adjudicated according to memo. according to feedback, those still pending were due to some technical problem, for example, one WOMer's PD was mistaken and all the calls turned to nothing. another WOMer's FBI response was missed from USCIS's computer.
so if you are pending for too long, and out of confidence in USCIS/FBI, they WOM will be good choice. See lots of example, see http://www.donkeyroad.com/wom