change default role of summary from heading to none
It is starting to become clear that the summary element will be the interactive part of the details/summary disclosure widget.
in this case it needs to convey useful name/role and state information to AT.

below is the info i sent in response to question for advice on summary/details implementation:
the key points are that depending on the platform accessibility API the summary element will have a different role, as an interactive control it needs to convey that interactivity not a heading semantic.


http://lists.w3.org/Archives/Public/public-html/2011Feb/0238.html:

in order for the details/summary to be accessible to people with disabilities it needs to be hooked up to be able to receive focus, be operable with the keyboard and have role, name and state information exposed via accessibility APIs

below are some suggestions these:

I  would suggest the summary content act as the label for the disclosure triangle;
Clicking on the summary with a mouse will open/close the details element.
The summary should be keyboard focusable and when the spacebar is pressed it will open/close the details element.
as should a tap on a touch screen.

The summary element should be mapped to AXDisclosureTriangle[1] role in the Mac accessibility API.
the accessible name (AXTitle) for the disclosure triangle is the text content of the summary element.
when the details element open attribute is present, set  AXValue property to 1 on the summary element. 
when the details element open attribute is absent, set  AXValue property to 0 on the summary element. 


On windows where there is no disclosure triangle role map it to the ROLE_SYSTEM_PUSHBUTTON in MSAA [2]

the accessible name (accName) for the button is the text content of the summary element.
when the details element open attribute is present set  STATE_SYSTEM_EXPANDED on the summary element. 
when the details element open absent is present set  STATE_SYSTEM_COLLAPSED on the summary element. 


[1] http://developer.apple.com/library/mac/#documentation/Accessibility/Reference/AccessibilityCarbonRef/Reference/reference.html%23//apple_ref/doc/uid/TP40001082-CH1g-BAJGFBAF
[2] 
http://msdn.microsoft.com/en-us/library/dd373608(v=VS.85).aspx
http://msdn.microsoft.com/en-us/library/dd318466(v=VS.85).aspx