I looked this up on Wikipedia and it's called the Euphemism Treadmill, which means you keep introducing new euphemisms that don't sound offensive, but since they are about an oppressed group, people end up using them as an insult anyway until they become offensive and you have to get another euphemism.
I just really think this is stupid. We can't just keep moving around and using a lot of different terms. I think retarded is a pretty good term because it says what it means--it means "held back." It makes sense--if you have a person who can't go to college because of their impairments, or a more severely disabled person who doesn't have the ability to talk very well, it makes sense to describe those people as delayed because there's nothing wrong with them--they just have the skills that most people, on average, have when they are younger.
I think it's a good word, and I think a lot of the words that are being used to replace retarded are actually worse. Like, "developmentally disabled" is not a word that you should be using to describe people who are retarded because it also describes autistic people and people with cerebral palsy. So basically, in your attempt to not offend retarded people (who in my experience are usually not that offended by the word retarded; it's other people who are offended) you end up saying that ASD and CP people have a different disability than we really have because you've reduced the term "developmental disability" to meaning retarded.
I just think it's really inaccurate, and strange, because you should be specific about the kind of disabilities people have. I mean, one of the hardest things about having ASD and/or CP is that sometimes people assume you have an intellectual disability when you really don't. When people use "developmental disability" as a euphemism for retarded, I feel like they're expressing that they don't care how ASD and CP people feel when we're assumed to be retarded.
The other thing people say is "intellectually disabled," which is just going to become an insult too, and also sounds REALLY euphemistic. I don't know how anyone is going to say with a straight face, "My brother is intellectually disabled." You're going to start saying either special needs or retarded because intellectually disabled doesn't sound like it describes a person; special needs and retarded have a more casual sound.
I also think "intellectually disabled" is kind of reductive. It reduces people who operate at a different level to people who just can't do as well on an IQ test as someone else. When really, people who are retarded (in my experience), are different from the average person in a whole number of ways, many of them positive ways. "Intellectually disabled" makes it sound like that's the only thing to them, that they can't do as well on a standardized test as I can.
I understand that we don't want to sound rude by using the word retarded when it is often used as an insult, but that's just bowing to pressure. I haven't stopped calling myself gay because people use the word gay as an insult; I haven't started calling myself "heterosexually challenged" or something. It seems like what people need to do is step up and say, "You can't use that word as an insult, it's wrong. It insults real, good people who happen to be retarded," and keep using the word retarded correctly. Because if you keep moving from euphemism to euphemism the reason it becomes an offensive word is because of ableism, and that isn't okay. You should be trying to discourage the social problems that it comes from instead of moving around and using different words as if that's going to make a difference.
(Update: I have now switched over to "intellectually disabled" a lot of the time. I freely admit I'm bowing to pressure and I still have a problem with the fact that I'm expected to do this, but I don't want to make people uncomfortable.)