Aikido, in a simple yes or no answer, can be effective in real life. I think it's ridiculous to totally say it is completely useless. You can read stories of people using it in real life self-defense. It is possible yes. But, that is the simple answer.
A more complete answer gives you a complete picture of Aikido's strengths and weaknesses as a self-defense art. If you can accept it's strenghts and weaknesses then Aikido can work for you.
The best way to assess Aikido's potential in self-defense is to observe Aikido black belts. What do you see? Do you see someone that looks weak or strong? Where is he strong? Where is he weak?
Aikido's Strenghts: Good, quick, agile, footwork. Good, varied, throws. Pins to the ground that are hard to escape. A focus on non-violence and minimal injury. Throws and pins practiced from a kneeling position. Wristlocks. The option to break an arm or throw an attacker forcefully if need be. Training in the jo and bokken (a 3 ft. stick and a wooden sword). Defenses against knife, club, and gun. Defenses against multiple attackers. Breakfalls to land safely on the ground. Randori that helps you practice your throws spontaneously against another student. A focus on self-defense and not just sport. The use of "ki." Control over your attacker. Atemi strikes.
Aikido's Weaknesses: No full-contact, realistic, sparring or competitions. Is very complicated art to learn, it takes a long time to be skillfull in it. Does not teach you how to deal with being hit,. Has very little groundfighting ability. Requires precise application or a throw or lock may not work. May not provide you with enough confidence against an attacker. Does not emphasize getting in good fighting shape.
So, from all that, what is being said about Aikido? Aikido is good in theory. It has a nice image of throwing your attacker and putting him in a pin, no blood, no mess. But, the reality of an attack may be much different. What happens if your attacker nails you with a punch to the face? You have never learned to take a hit in Aikido. Will you just give up or be able to fight back? What if the attacker isn't "cooperating" well enough and your wristlocks and throws are hard to apply? What if he is just too strong and muscles out? What else in your Aikido training do you have against him? What if the attacker takes you to the ground? Aikido has virtually nothing to prepare you to defend yourself on the ground.
If everything goes right though your attacker will be thrown down and pinned. The situation has to be ideal enough to do that though. A black belt Aikidoka has great skill. He is capable of eventually getting most attackers in a pin. After 8 years of training he has some well earned skill. If you allow a black belt to demonstrate his wristlocks and control over you is very good and impressive. The sheer demonstration of that power shows it can be applied in real life someway.
But, everything needs to by the book for an Aikidoka. If his wristlocks are being easily broken, he is being overwhelmed with an avalanche of punches, he is too afraid or angry, he is wrestled to the ground, his throws are not working, what is he going to do? Aikido has a limited amount of skills. It isn't like some martial arts that have a wide range of skills: puching, kicking, clinch fighting, throws, groundfighting, etc. It has just wristlocks, throws, some simple strikes, and the pin. If things are kept where the Aikidoka can use his skills best then he has a good chance. If he is put in a situation where he has no training or very little, he will have to improvise outside of his Aikido training. His Aikido training alone won't provide answers for him.
It is hard to deal with someone being violent with you. It is hard to be violent back to someone too. Unless you are someone who is "comfortable" with violence, this is a tough part of an attack. You have someone maybe yelling at you, cursing at you, making threats, or they hit you without warning. You immediately have that adrenalized feeling of fight or flight. You will either drawl up like a turtle and try to survive or you can go animal and try to rip your attacker in half. These are some of the realities of real-life violence. Will Aikido train you for that? Ideally Aikido teaches you to have a very calm mind in an attack. Maybe you will, maybe you won't.
Aikido can be effective but, it has it's limits. If that is ok with you then, ok, take it and make it work for you. But, a lot of people think it is ineffective for the average Aikido student. I say it can after 3 yrs. to 8 yrs. of training but, it needs to stay away from being a wrestling match and your you need to have a tough, confident, mind that can improvise if you Aikido doesn't go as planned.
An art is only as Effective as the artist. What is your motive? Glorious battle, victory, honor, beauty, health? Aikido is no better than any of the others unless it suits you. Watch some videos about it, read some too, everything you read here will be opinions, which can't help you much.