It isn't just Safari. In the begining, I thought because Mac uses "Preview" to open pdf files, that having my Mac users install the Adobe Reader would fix the problem. For most of the interactive stuff, including embeded flash apps, it did. However, the submit by email problem wasn't. Something about the code used for the button doesn't work on the Mac OS. I REALLY would like a work around aside from having Mac users print out the form and snail mail it.
I tried the above suggestion of using a regular submit button and it didn't work either.
I'm a new Mac user who just discovered this issue when developing a form for a site I'm working on. Thee is a handy solution (on Snow Leopard, anyway, I haven't tested on another OS). On a Mac, if you fill out the form then crtl+p you bring up a print dialog with an option in the lower left corner that says PDF. If you click that option one of the options available on the resulting drop-down is Mail PDF (this is actually an option on just about anything for MAC). Selecting the Mail PDF option opens your email editor of choice (pre-defined) and inserts the filled out form in the email. You can then send it to any email address you choose. This means that all you have to do to enable Mac users to fill out the form online and submit via email is make sure you provide an email address for them to send it to. Hope that helps.