The feedback form is one of the hardest things to get right IMHO. We've tended to use paper feedback forms as despite very few people take the time to fill in online surveys after the event.
We recently tried a mixture of quantitative and qualitative questions for a series we ran this year. The idea being that we'd give attendees ample opportunity to say what they felt but also try and get some metrics back (i.e. 1-5 rating style questions) that we could use in post-mortems as some kind of guide for moving forward.
Here's a screenshot of what we ended up with: http://cloud.keirwhitaker.com/2y3P2Y2e3i2u
Overall it worked well. Of course, we got the usual silly comments (sandwiches were too cold, chairs were too comfy etc) but the response rate was > 50% for all events.