What is the most simplest way to push text to campaign member description notes in SFDC campaign from a Form Fill embedded on a Marketo LP? Any ideas would be greatly appreciated.
So the "simplest" way is never going to be simple.
The options are:
You are entering Salesforce area here but..
Try creating a hidden text field on the LEAD object in Salesforce and use a Formula field on the CAMPAIGN MEMBER object to copy the value from the lead to the campaign member as, as Sanford says, Marketo doesn't write to the campaign member object atm.