Not exactly. Rather, PC malware that would be harmless to the blackberry but could infect your PC or worse, spread to your enterprise servers. Formatting the card in the blackberry before you connect the bb to your PC neutralizes the threat. If BES systems start getting compromised, you can be sure that BES admins will begin implementing IT policies that disable Media Cards.
Posted from my CrackBerry at wapforums.crackberry.com