Slashdot reports on a coffee shop that has started turning it's WiFi off on weekends. WiFi "squatters" were sitting at tables for six to eight hours at a time, preventing other patrons from finding a place to sit, and worse, some squatters were not buying anything.
It might be that some clearly posted rules would also mitigate the squatters, and it's an interesting contrast to other published reports that some businesspeople have seen receipts and profits rise after installing WiFi.