Just thought I would toss this into the pot. I read an article from Rickson Gracie (I think). Anyways, he was talking about the best self-defense in America is to buy a gun. He said that in Brazil GJJ is the best because fighting is still "honorable". Both sides will gather around in a circle and watch the two people fight it out.
He said in America that doesn't happen, the other friends will jump in and he admitted that going to the ground is not a good idea and something else is needed.
Like alot of people have said, all arts have strengths and weaknesses. What many people fail to do though is look at different attacks and find viable solutions to those using the principles and concepts in their art. Then what we get is a "jack of all trades and an ace of nothing", they study lots of different arts for a short time and never understand the deeper principles behind it.
Yes, aikido has "weaknesses" but by understanding those you can overcome them and negate them when you put in the time to understanding the art as a whole. But, to make a blanket statement that it does not work is just as erroneous as saying that aikido is the best there is in martial arts