We use it for different reasons, sometimes just for a specific department, sometimes for the dealership, and sometimes across the company. It's a good way to get quick responses that are easy to analyze.
I really can't think of any -- even when I have issues or questions on how to do certain things in creating a survey, I have received quick and helpful support through chat/e-mail.
None -- I was lucky enough to have received recommendation to use SurveyMonkey from the beginning and had no reason to use anything different. The price was right and the product was good.
The product is well designed and easy to use -- where I've had difficulty is when I'm trying to get a brand new user started on creating a survey when he had no idea what a good survey should look like and what type of questions should be used to receive the most useful type of responses. If there is a quick "helpful tip" type of information provided, it might help the new survey designers get better results from the very first time....