After installing Adobe Reader 9.0 I tested it at the forms page for irs.gov. I have my settings so that display of a pdf in Safari utilizes Adobe's plugin.

The requested form, 1040ES, displayed but I received an alert telling me that certain features were not enabled in Reader and, after filling in the form, I could print but not save the document. A dialog also appeared at the top of the document advising me of the same.

I attempted to find where, in Reader, to turn on these features but could not. I then removed Reader 9 and reinstalled Adobe Reader 8.1.2 as well as its current update. Things returned to normal.

I have filed a bug report with Adobe.