If you depend on cheap broadband connections, you must consider the appropriate use policies (AUPs) of your broadband providers.
There are already laws on the books that restrict the sharing of cable bandwidth?cable companies have been dealing with the issue since the birth of their industry in the 1960s. AUPs may not need to spell out restrictions explicitly covering the sharing of Internet access with neighbors. Also, the cable industry specifically has 802.11 on their radar; see http://www.spectrum.ieee.org/WEBONLY/resource/apr02/webs.html for details.
Cable providers are scared of NAT, which gives ISP customers the ability to add additional computers to an internal network without applying for additional IP addresses. Cable providers are proposing an alternative to NAT that would allow them to see the actual number of users behind a NAT box and account for a customer's usage of their network.
DSL providers are also concerned about oversubscription to their low-cost services. Bandwidth is expensive, and a $50 monthly fee will not cover the cost of a 1.5Mbps DSL going flat-out, 24 hours a day. There is a very good chance that broadband providers will start to charge for extra bandwidth, cap the bandwidth, or be time-sensitive in the usage.
Some Internet providers make no limitations and actually encourage "reselling" of the connection. Normally you will have to pay a premium for this service. Check with the provider for restrictions.
Here's a sample of an AUP with no restrictions:
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