This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Or, do one better and actually feed the data straight into Excel, where the user can save it in the usual way. Instead of "text/csv", make your MIME type "application/x-msexcel". DON'T generate HTML, BTW, all you need to write are lines of comma-separated text, just like you would from a regular application.
Customer surveys are for companies who didn't pay proper attention to begin with.