I think there has been some very good responses so far. :asian: Although I am surprised we haven't seen theletch pop up yet.
My sensei and another one of our blackbelts are both cops and I know they've used Aikido (yes, even the joint locks) in the "real world". I'm in a situation where I've had to use Aikido on a mentally ill person who went beserk, and I used it to control them without causing injury until he calmed down enough to be "normal" again.
I think Aikido is great for defense when trained properly. But sadly, there are many Aikido dojos that don't use strikes or practice with ANY resistance. They're the ones that I think would get a "rude awakening". In my dojo we practice strikes, randori, and we spar.
That being said, if a friend asked me that they needed to learn effective self defense quickly, I wouldn't point them towards Aikido. Aikido takes a long time to learn (especially if it's your first martial art) as there are so many tiny details, and even longer to know when, how, and on whom to use which techniques on. When I was a beginner, I thought once I "learned" a technique I could use it on anyone and anytime. Now that I've been in it longer, I realized that certain techniques work better with some body types than others. For example, there's a BIG guy in my dojo and when he comes at me and strikes Shomenuchi with a lot of force, it's much easier and more practical (for me) moving offline and going into an Irimi (or another technique like kotegaieshi) than a Ikkyo (omote, especially). Sure there are people who can "make" a technique work, but there's a difference between flowing into a technique or being a bull-in-a-china-shop and trying to force something that isn't there from the beginning. That also goes leads into the whole concept of not "planning" a certain technique, but going into the most appropriate technique for "whatever" the attacker gives you!
Robyn :asian: