You should consider changing the data type for the user_answer field in the surverys_result_answer table. The text(255) doesn't match well with the comment field on the survey form. The users can type in more text than 255 characters, which then gets cut off in the database. With disk space so plentiful these days better to use a BLOG data type and let the users type as much as they want.
Otherwise a great and very useful plugin.