My article on "Enabling PDFs for User Input" is now available at http://www.front-runner.com/tools_and_resources/articles/enabling_pdfs.html (with links to sample PDFs, demonstrating different approaches).
Shlomo Perets MicroType, FrameMaker/Acrobat training & consulting "24 easy ways to improve your PDFs with FrameMaker-to-Acrobat TimeSavers/Assistants", http://www.microtype.com/ImprovePDF.html