News.com's Richard Shim pulls together several related threads about the risks and liabilities of Wi-Fi networks in light of recent arrests: While there's not a simple connection between you leaving a Wi-Fi access point open and someone committing a crime across it, the recent child pornography and brain-dead IT department network exploitation arrests are causing a lot more discussion.
Because Wi-Fi networks aren't straightforward to secure now, the risk of lawsuits is low. This doesn't address purposely open APs in community networks or free networks either, or legitimate users who have paid to use commercial networks who then commit criminal acts!
Interestingly, Lowe's customers weren't hurt by the fact that three men apparently were able to gain easy access to their Wi-Fi networks in several places and insert a credit-card-collecting crack into the system. Because Lowe's has a corporate IT operation, I would imagine Lowe's would have been liable for negligence if customer information had been misused. They should have known better.