From HTML WG Wiki
Recent Research on Users
On February 28, 2011 WebAIM released the results of their latest independent user survey which asked a question regarding the longdesc attribute.
The majority of respondents declared longdesc useful. The report states:
These responses show a strong usefulness of the longdesc attribute, which is currently under debate for omission from HTML5. Also of note is that 22.7% of respondents do not know the usefulness of longdesc, suggesting a need for better education or presentation of this functionality in screen readers.