Hail! 
Just to quickly square things up a bit here (And speaking as a member of the Hacker/computer enthusiast community) please be advised that accessing a wireless network for any purpose
without the express prior consent of the owner of said network is an offence under the
Computer Misuse Act 1990CE (As amended) within the United Kingdom. Similar legislation may exist in some other countries as well. 8)
When accessing another person's wireless network, you are actually connecting into their own
personal computer network (Normally at their home) and are therefore implicitly obtaining access to all resources on said network - Including computers, printers, scanners, NAS devices and so on.
Even if you only intend to obtain a route through to the Internet and access nothing else on that network whatsoever, you are still joining another persons
private network without their permission, which again can constitute an offence.
Please be aware that under the
Computer Misuse Act, it is not a sufficient defence to plead that
because the network is "unsecured" or "open" to access, then all comers are implicitly invited to connect - The CMA takes into account the rights of less technologically aware users who may not know how to secure their networks properly, or even that their networks should be secured in the first instance. Although prosecutions for unauthorised wireless access under the CMA are fairly rare, they are certainly not unheard of...Do a Google search and ye'll probabally dig up several case studies!

hock:
The only networks that can be considered "
open to everyone" are ones that have no encryption whatsoever,
AND have an SSID (Or message sent to thy PC during a network scan) that clearly permits and invites public users to connect to that network. SSIDs like "Free_public_access" and "Costa_Coffee_PUBLIC" can fit under this heading, but ones like "Hants_Library" and "Caffe_Macchiato"
don't, as they only identify the site/network
name and don't openly invite public connections! 8)
A friendly security warning:
Finally, I would advise people to be
very careful when connecting to a wireless network that they do not own and fully control, as the potential for thy data to be stolen through this "untrusted" connection is very high.

hock:

For example; It's both possible and very easy for me to set up an open wireless network called "Free_public_internet" or something similar (Default names like "linksys" are best for this) at home which feeds into my home broadband connection for Internet access, but also has a machine running on the same network that captures and logs
everything that's sent across the connection - Including encrypted SSL traffic that I could crack into unencrypted data at my convienience. Anyone connecting to this "free" network of mine would be exposing all of the data that they're sending/receiving to my eyes without even realising it...Including the content of every e-mail, every photo, every webpage and so on.


:?
Funniest of all though: As this would be my own network (And thus my property) then IIRC I would not be breaking the Law at all if I did this, especially if I were to warn the user (Through injecting outgoing HTML etc.) that their traffic may be recorded and analysed "for network maintenance purposes"...

hock:

Farewell for now, and hope that this helps ye all to understand the legal standpoint and high security risks of "leeching" wi-fi...
>> Death <<