Yes, I have, several times.
Aikido is a defensive art, that uses another persons strength against them. I would rate it 5/10 for self defense on the street. Why? Because it does not involve sparring, so your not going to be conditioned to take punches. Lets face it, thats what a mugger/attacker/drunk does - he hits, first and usually hard. If there was an option to study krav maga instead, or as well as, I would do that.
Just like most martial art styles, if you're proficient enough in Aikido, a punch or strike will never land. Now if somebody sneaks up on you, there are ways of reacting immediately to his/her initial contact. That is, you may not see it coming, but are able to evade and neutralize the strike just as it initially makes contact before it has a chance for the strike to follow through all the way. Easier said that done, yes I know, but I have seen it done and have done it myself.
I love Aikido, especially when it comes to taking care of business when you have 2 or more attackers. I've been in some situations where I've had to fight 2 or more guys at once. Long story as to how it happened, but I got jumped walking out of a second job I had at one time that was in a bad neighborhood. I ended up using some Aikido moves and had one guy on the ground within seconds, and was able to get the other guy down on top of him almost immediately after where neither one of them could get up until I let them. Nobody was hurt which was the best thing about it.
To your point though, I think it's always good to train to learn to be able take a punch just in case. Krav Maga is a very effective art. I mean it's made popular by the Isreali Airforce, who are the toughest SOBs only second to the US Navy Seals.
Anyways, yes, being able to take a punch is importantr. It's like when some big ass dude throws and lands his hardest punch at you to the point where he knocks your teeth out, and you just look at him and smile. Then again, I'm the type of guy that if a person chops off my arm, I will pick it up with my other arm and beat the hell out of that person a bunch of times before I finally go down.
I'm both a lover and a fighter, but I'm much more of a lover than a fighter though, so I'm all about avoiding those situations as much as possible.
Jason Salamone