Also, the assumption that everyone wants to share their last name, or that every one has a last name is erroneous. Some people really don't have a last name (esp. the place I am from there are lots of people with just one name). You might want to change the form to just a "Name" or make last name optional. Unless of course you are legally required to not do so.
You don't have to share your actual last name. Pseudonyms are fine. I didn't think about the case where someone doesn't have a last name. I might need to do something about that.
