Are hot spots hot beds of illegal pirated filesharing? Yes and no: There's no way to know and no records are kept at most locations that share network access, including private individuals and public parks. Although the RIAA and others could track down a location, they'd have a hard time holding someone responsible who didn't actually perform an illegal act, but was just running a wireless connection.
Interestingly, if you're acting like an ISP, the Electronic Frontier Foundation's Fred von Lohmann argues that you should also get the same protections as an ISP. Lohmann contends that individuals and businesses that operate open Wi-Fi hot spots should be eligible for the same legal shields that ensure that ISPs aren't liable for the online actions of their customers.
(Disclosure: The EFF is representing me and four co-plaintiffs in the Newark v. Turner et al lawsuit involving digital television recording.)