Every time you step into any establishment, you need to find the "Free Wi-Fi" decal somewhere in the building. If it's not there, leave. It's 2013 and if a company wants your patronage, they should do the right thing and offer you a way to browse the Internet gratis.
For those of you being extra cautious with how you circulate your money (read: can't afford the muffin/cup of coffee required to keep your seat), you have other options. Go to your friend's house and demand to know the Wi-Fi password while raiding his fridge. If you want to enjoy free Internet in the comfort of your own home, know that many of your neighbors don't lock their networks. Relax, it's not really stealing. It's the 21st century equivalent of borrowing a cup of sugar.