I stayed away from this one for a while for several reasons ( not the least of which the fact that it took days for Comcast to respond, then repair their lines. ) But since it is still going, I have a few thoughts on the matter, though I am no expert.

First, to respond to nihil who asked
So, your "theft of services" is the same problem? "THEY" don't actually have a proper crime on the statute books?
In New Jersey
N.J.S.A. 2C:20-8. Theft of Services.
a) A person is guilty of theft if he purposely obtains services which he knows are available only for compensation, by deception or threat, or by false token, slug, or other means, including but not limited to mechanical or electronic devices or through fraudulent statements, to avoid payment for the service. "Services" include labor or professional service; transportation, telephone, telecommunications, electric, water, gas, cable television, or other public service; ...
In response to something mohaughn said
How many people here think it is perfectly legal to walk into a public place of business, and hook their laptop into the rj45 connection sitting behind the water cooler? It may not get you arrested, but as soon as somebody in that office sees you sitting on the floor with your laptop hooked up to the wall they are going to ask you what you are doing. Same thing applies. There is no sign that specifically says you don't have the right to use this, but there is nothing that would give you the impression that you have the right to use it. In some cases, you probably would get arrested depending on how the office workers wanted to treat you.
XTC46 said
actually this would be tresspassing. And I wouldnt be so sure about people questioning what you are doing...or atleast not caring. Its amazing how far "Im here to fix the computers" will get you until somone with even a little knowledge will call your bluff.
That is totally incorrect ( at least in New Jersey ). It was a public place ( key word here is public.) The person was a member of the public and thus entitled to be there ( they did not say the business was closed, did not say the person was not authorized to enter, nor that the person surreptitiously remained within. ) It would be Theft of Services, maybe, see below.

This highlights several problems when attempting to prosecute someone: what law exactly did the person violate? Did the person damage files? Obtain information such as credit card numbers, bank account numbers, etc.? ( again, see below.)

The ECPA ( Electronic Communications Privacy Act of 1986, this amendment affected several sections of the law ) that Negative referred to is very complex to say the least. Although he covered it rather well so briefly, to say that one connecting to an
Open network, and you connect to it unintentionally: nothing illegal about that
would depend greatly on who's network and what the person did when they realized they were connected, what frequencies they were listening on, etc. Again, very complex.

And who is allowed to enforce? Well, there again, it depends what applicable statute was violated in the U.S. Code, but for the wiretap, basically any law enforcement agency including local government, but do they actually know that?

Would Barney Fife know what statute or code applied?
Would he ( now, not when the show was written ) be trained for such things?

Obviously ( as in the case of N.J. as described above ) a case could be made for theft of services if one attempted to access the Internet via the connection, because they are now using services described which they are not entitled to. But who is the victim? The cable company? The subscriber?

What about ( as mentioned ) someone who intentionally leaves the network open for others to connect to? Without knowing the subscriber's intentions and contract with the ISP it would be hard for any law enforcement officer to bring charges.

I suppose their best recourse would be to at least detain the person for identity purposes and confiscate all equipment as evidence. Remember, law enforcement, at least here in the U.S., don't need to prove anything immediatly, just have Probable Cause. And the probability in a case such as described ( in the article ) is they violated either the ECPA or committed Theft of Services. Proof would come later, after the equipment was properly examined and a proper investigation was done. But each case would have to be judged individually.

Even if the proof was not able to be obtained, how useful do you think that laptop would be by the time the person got it back? ( Remember, it could take years to do so. ) Are you willing to chance losing that shiny new laptop?

Just my thoughts.