To add to Southpaw adding to cmhbob, if you have a WordPress.com site, you can change the comment settings through your WP Admin portal. Two of the options are:
Comment author must fill out name and email
Users must be registered and logged in to comment
I disable these, so that people who wish to comment don't have to be 1) registered with WP/gravatar, 2) use any other blogger credentials, or 3) even leave a name/email address to comment. Random/anonymous users can comment. Akismet filters most of the spam comments I get, but then, I have relatively low traffic right now—about a thousand views per month on a good month. For busier sites, this might not be as feasible.