>Login requirements exist for one very simple reason: making sure the reporter can be contacted for the inevitable follow-up questions. "What OS are you using? What version of [product]?" etc. It's a barrier to hit-and-run bug reporting where a brief, useless report is placed with bogus or absent contact details that prevent follow-up. Sure, you could just close them, but there *is* a balance needed between time of project contributors and time of bug reporters.
Just ask for e-mail (maybe first and last name) and then send a confirmation message. Launchpad does this.