It's my opinion that aikido does work. The problem is that many people who study aikido are not natural fighters or are not committed enough to serious training (and I don't mean they're not sincere at what they do) and, therefore, are at sea when it comes down to "real" situations (this applies to all MAs).
A lot of people start aikido for self-defence reasons -- at least most of the people I've met -- not simply as a way to enlightenment (that comes later). Also, many of these people start aikido because they find the other MAs inappropriate for them. It's a bit like "why are there so many unhealthy looking people in a health food store? -- that's the reason why they're there"
I found it very difficult to make the decision to train in aikido, mainly due to the classes and students that I saw. I could tell that it was effective and liked what I saw, but I couldn't understand why so many senior students looked so, geez ... clumsy and unatural -- lacking confidence (I wish I could find better words to describe this). What convinced me to start were the "few" who I thought were very good at what they were doing (exclusive of rank). No hollow talk or facade there!
Aikido works, as do all martial arts. However, the average student is just that: average. Should they quit? Of course not. Should they strive to be better? Well, that's their decision.