Since at some point spammers will find your site and create splogs, there’s many ways to stop them. Deleting them as they occur is like shovelling snow during a blizzard. You can add another field to signup, add a captcha, go invite-only, or in the case of my main niche blogging site – moderate the signups. This works well for smaller signups where you don’t get a huge number of new bloggers on a daily basis, and where spammers have proven to be a general nusiance, a potential embarrasement, as well as a time suck.