I still routinely encounter fillable forms that Preview.app can't handle, particularly with checkboxes or large text areas. It also frequently uses the wrong font in PDF forms meaning text doesn't fit in the prescribed form fields.
I agonized about installing Acrobat Reader, but Suspicious Package says it wants to run 88 install scripts. I don't feel like tracking down that much malware when I uninstall it after filling out a form.
Go Foxit!