Spammers went after Twitter pretty hard this holiday weekend using the "friend invite" model that was first developed against other social networking services. Briefly, the attack involves creating a large number of spammy profiles and then inviting people to view the spam by performing a friend request, or in twitters case, "following" the spam target. I have included screenshots of a few of these attacks.
An individual can remediate this attack in the short term by disabling e-mail notifications of people following you. This is by no means an optimal solution. The only people who can really address the situation is twitter, through a combination of blacklisting, throttling, CAPTCHAs, and content analysis.