If you create a fillable form in Acrobat, other Acrobat users will be able to fill out, print and save the form. Not so with Reader users and there are far more of those. Reader is free, easy to install and there is no reason for anyone not to have it. In order to make forms accessible to Readers only one small additional step needs to be taken.

In Acrobat 9:

Create your form. When the form is complete, go to Advanced => Extend Features in Adobe Reader…

Extend Features in Adobe Reader

This will prompt you to save a copy. Be sure you do, it will restrict editing later on.

Enable Usage Rights in Adobe Reader warning

When the file is opened in Adobe Reader, there will be a purple bar across the top of the screen letting users know they can save data typed into a form.

Adobe Reader view of a usage enabled form

Simple as that! Take this one extra step on all of your PDF forms to let Reader users save them.