InDesign CS5.5, brings with it several improvements. Several that  you don’t have to do anything about. They’re just there, and work! You can continue using the same workflows.

Accessible PDF documents is one such area. You can create accessible PDFs for Adobe Acrobat, Adobe Reader, or other software such as screen readers. InDesign CS5.5 automatically adds tags for the following:

• Tables and nested tables
• Lists and nested lists
• Footnotes
• Hyperlinks

If you have an InDesign document that has the following structure:

InDesign Document snippet

The following images show the tags exported by InDesign CS5.5 (viewed in Acrobat Tags panel).

Table tags

Nested list tags

FoootNote tag

Hyperlink tags

Note: The THead, TBody, and TFoot tags are honored only if you export to PDF version 1.5 or higher

See Adobe InDesign CS5 accessibility overview

Update( April 13) : I wrote another post about how Articles can be used to specify Reading Order. You might find that interesting as well.