Disabled doesn’t mean people in wheelchairs or with white canes. Everyone has differing levels of ability in different senses – accessibility isn’t a minority thing.
Permissions and trust – I can tell from looking at a page if I trust it with my e-mail address etc. How does a JAWS user make the same judgement?
OpenID authorisation uses redirects – problematic for phones and screenreaders.
Dopplr (hi Fiona!) – importing/exporting friends lists is not very accessible. Not sure I follow this one.
Many people need plain english – how does this sit with EULAs and terms that you agree to when you sign up to a service? CC has a good model for simplifying legal bumpf.
Increase accessibility by allowing export to a wide variety of formats. Give users choice.
Use the correct stack. Joost uses SVG with HTML and script. Unfortunately, the product itself sucks.