Unspam makes it harder for spammers to automatedly send spam to your blog by changing the names of the fields in the comment forms.
There is currently no configuration available on this plugin, just install it and activate it and it will start protecting your blog.
No. I hate CAPCTHAs as much as the next person, this plugin does not use them. Future versions might include the option to enable a CAPTCHA if you really want one.
Nope, spammers just have to prove that they're NOT human. We give the spammers enough rope to hang themselves with.