Do I have to have an account to use blekko?

No. If you wish to use blekko to search, you don’t need an account. If you wish to create your own slashtags, see SEO data, mark websites as spam, or see your Facebook /likes data, then you will need to have an account. You can create an account either directly with blekko by signing up on the join page or you can login using Facebook Connect.