We already knew that peanut butter was bad but...

The FDA issued a warning not to eat peanut butter from the brands Peter Pan Peanut Butter and Great Value Peanut Butter purchased after May '06 because there is a chance those have been contaminated with Salmonella.
Here is the warning:
http://www.fda.gov/bbs/topics/NEWS/2007/NEW01563.html
If you eat a lot of peanut butter and get paranoid here is a Q&A:
http://www.cfsan.fda.gov/~dms/pnutbuqa.html
Salmonellosis:
http://en.wikipedia.org/wiki/Salmonellosis#Symptoms