Great looking plugin although there is a couple of things which I think would make it better. These may be usage questions though, if I'm missing something... :)
1. Ability to customise the colours used by the Google Chart API. Depending on your number of options the orange colour can get pretty similar.
2. Aligning the Google Chart title. On questions with longer titles the title misses bits from the image generated through the API.
3. There seems to be a bug with the Likert type. There is a few threads in this forum showing the error (such as: http://wordpress.org/support/topic/plugin-wp-survey-and-quiz-tool-likert-questions-error?replies=1)
4. When using the Likert type allow for the user to customise the scale, such as 1-5 rather than 1-10, and perhaps substitute for other values like Agree, Strongly Agree, Disagree, etc.
5. Allow for longer Questions in the Quiz, currently they are capped at 255.
6. Ability to remove scoring feature. It makes a lot of sense for having a scoring system in the Quiz, but when the type is Survey I'm not sure it is as useful and could be simplified by having an Option to disable it where appropriate.