http://twitter.com/#search?q=%22today%20was%20so%22

The posts started a few hours ago, stopped for a while, and just recently started again. It may be that a 3rd party service was compromised, so if you've given your twitter credentials to another web site, it's worth the time to change your password. The volume (many thousands of accounts, including people I know who would not be inclined to sell posts) and nature of the posts seems to rule out the possibility of a paid posting service.