I see many many people quote a rate of 90% denial for first round in the application process as standard when applying for disability benefits.
I'm not entirely sure where this comes from, but I have a couple ideas:
Many people are much more likely to be vocal about being denied benefits than being approved, for various reasons- including getting a lot of crap for being approved.
e.g."Why did you get approved? You don't seem that bad.", which I have personally experienced and observed.

Also, approval rates vary depending upon what stage of the application process is being referred to. At one stage it is estimated to be about 10%, but the initial stage is about one third.

Approval rates also vary by state.

An annual statistical report on Outcomes of Applications for Disability Benefits is available through 2010.

One of the more relevant charts in the report:
Chart 11: Final outcome of disabled-worker applications, 2001–2010

I just thought maybe this was a good idea to bring up for discussion?