Hi Bec R,
As of a couple weeks ago, the Marketo team was still working on fixing the underlying javascript bug that was causing those javascript functions I mentioned above to fail in their Forms 2.0 script. I'm not sure what the current status is now, as we had waited a month for a fix, when Marketo support informed us work on the fix was still in progress, and kindly suggested we try a workaround in the meantime, which was to use a bolean test ("is" or "is not") instead of a regex test ("contains", "begins with", etc.) on the fields which we are now successfully using to determine the visibility of our form's fieldsets.
This worked for us, thankfully, only because the simplest test necessary to create our particular visibility rule just happened to be a bolean one (yes/no), versus a regex one (such as testing whether the contents of a field begin with the letter "J").