There are quite a few issues with Stack Exchange sites and accessibility for screen reader users. These include but are probably not limited to inability to tell whether elements such as vote up and down are clickable, inability to accept answer using a screen reader, inability to easily vote on comments, not having access to important functions such as vote up and down from the keyboard, etc. Are these issues the developers are interested in fixing or is accessibility not a priority? If the developers are interested in fixing the issues should I open a feature request for every issue I can think of, or do a section 508 style assessment to bundle everything together?
At this time, the Stack Exchange software is believed to be "accessible," mostly through anecdotal evidence.
Section 508 compliance is going to become a bigger issue as we work with more communities that are going to require it. If someone is willing to do a 508 compliance assessment, I would suggest compiling the findings into a comprehensive document and issuing a "Make Stack Exchange 508 compliant" [feature-request] with a link to the document for reference.
That's preferable to posting a few dozen obscure design oversights that few people will be familiar with nor care about directly.