I got diagnosed half a year ago at 20 years of age. I'd always had problems but my parents are old-fashioned and undereducated so I couldn't get an assessment until I had toe power to do so myself in adulthood. It started with going to counseling, another thing I was thrilled about having the freedom to do. The counselor figured pretty much straight away that there was something biological going on and recommended that I go to a specialist, so I spent months finding a psychologist and got a diagnosis fairly quickly.
I think self-diagnosis is questionable, yes, but it shouldn't be bothersome to anyone who is diagnosed. I can understand what it's like to worry about affording it, about the stigma, about whether the treatment is available afterwards and about the difficulty in finding a specialist in the first place. Adults have a lot of trouble getting diagnosed. I believe that my psychologist didn't do all the extra things like months of observation, asking the family etc. He expected that, in my adulthood, I'd be able to answer for myself, so family wasn't necessary unless I was unsure or couldn't remember. He saw me stimming, which I couldn't help as I was in a totally new place alone with a stranger. He also has twenty years of experience as a specialist in autism and related disabilities, as well as counseling.
In the months it took for me to find someone to help, my counselor gave me some information on autism and I started looking it up online. I found myself identifying very quickly with almost all of the Asperger's traits listed on every site I found and was becoming convinced that it was a possibility. This just made me more determined to have it confirmed and if I hadn't managed to get funding for the diagnosis I'd have "self-diagnosed" and started researching self-help strategies.
So what I want to say on this topic is that people who diagnose themselves, and start looking up sites like this one to get help, deserve the help they need just as much as the people who are diagnosed. Some of us weren't diagnosed in childhood because our families are clueless and stigmatize anything to do with mental health treatment. Some of us can't afford a diagnosis or treatment, and some of the people who can are miles away from anywhere that can provide those things. So what do you do when you're 99% sure you have Asperger's or some other form of autism? Get help in any way you can. It's not fair to put down others with the same problems who simply don't have an official diagnosis because they can't get one or because they don't feel that it's necessary.