Ben Sheets gave Brewers fans like me a scare Thursday. The good news, at least according to the Talking Brewers show (link to Brewerfan.net thread here), is that it's not that lat muscle he tore last August. Instead, another muscle is straining - overcompensating for Ben being on the shelf for a while.
A setback, but nothing serious. Thankfully.
EDIT: MLB.com has a more permanent link.