Yes, I even have the messages marked with a Label for when they come into my personal Gmail account. Sometimes they make it into my inbox, sometimes they are in my junk mail. My clients don't use a web hosted email such as Gmail though so they don't even get their junk mail messages.
I'm not sure what spam filtering service our email hosting service uses, but it's occurs with Gmail as well, so I presume it's not unique to any one service. I think we'll have to just record the survey results in the database and view the results from our CMS login.