Found this looking up info on Social Security and Depression. There's a link on this page with a discussion with an actual lawyer that is pretty revealing for anyone considering or in this process. Even though it is focused on mental illness, it applies to all disabilities.
There's also other links with more info on SS and SSI. I always find these links AFTER I need them.
http://depression.about.com/cs/ssa/a/socialsecurity.htm