I created several interactive forms that reside on an intranet; each form has a mailto: link that sends the filled-out form to two different email addresses. The form is for in-house use only, and everyone has email that works. The form works for most people who have Reader 7, but does not work at all in Reader 8. Some Reader 7 users report "The operation is not permitted" errors. Some Reader 7 users report there is no error, no nothing... it just sits there and the cursor blinks rapidly for a second.
For about 80% of the people it works fine. I cannot figure out why it doesn't work for everyone.