Xtr-X- As a matter of legal issues, there are two things involved in this.
1. Under the DMCA, a complaint can be lodged against a potential copyright infringer (or in this case copyright protection circumventor) and the ISP will be left with two choices: Respond to the complaint in a legal manner, or take the offending material down. Taking the material down immediately renders the ISP no longer legally responsible for the content, but places the responsibility on the poster. Making a response, depending on the nature, most likely leaves the ISP open to legal responsibility (IE allows them to be sued as well.) As a result, 90% of the time an ISP will chose to remove the material and leave the response to the individual accused of infringement.
2. Because of the high likelihood of someone maliciously using the law, there are two teeth involved in this: With the DMCA, invalid allegments of infringement can be handled as harassment, defamation of character, and a wide variety of other legal responses that basically mean "Counter-sue and win a good chunk of money." With the DMCA's nature, it's much more likely that when a countersuit succeeds there will be a larger judgement than normal, although this has yet to be tested fully in court. In order to take action outside of the DMCA, the person or company doing the suing will be required to file legally compelling evidence to convince the courts that sued individual is indeed guilty. Sure, I can spoof IRC logs. But any decent lawyer will point this out, and make that falsified evidence be unusable (at least relatively unusable) in court. As a result, you will typically rely on outside evidence such as packet logs, external IRC logs, server logs, and so forth- third parties that would have no interest in creating the evidence, and plenty of interest in not hiding the evidence (obstruction of justice.) Once again, falsified or insufficient evidence can lead to lawsuits.
Now, in terms of criminal prosecution, there are several factors that can be used in this situation, at varying levels of jurisdiction. Most likely if you're a US resident, you would be prosecuted in the US District courts. If at all. (Most likely, you would not. One crack is nothing. Drink or Die, tho, is another thing.) The exact crime that you'd be charged with is literally a VERY fine line thing. Chances are if you lawyered up you'd never see prison, but you'd get probation and a criminal record to boot.
As a result, let me summarize this:
1. An ISP will not hesitate in cutting you off in response to a DMCA claim, because in the long run that attitude will save them lots of legal trouble and money. I have worked in a networking office, and they're pretty quick to respond to these issues (I think the law allows them 30 days to respond, technically, but for safety sakes they do it asap)
2. It will then be your responsibility to sort things out, or accept the consequences and make an agreement between you and the other party.
3. Most of the time this is all that will happen. No lawsuits, no prosecution.
4. Look up DeCSS. This is an ugly example of what can happen when it goes further. Note that some people involved don't live in the US, and also note that the young kid who wrote the brilliant code is still in court settling this out- You know that can't be cheap to deal with. The kid faced both civil and criminal suits. AFAIK, they're both still in court, but the civil manner could be resolved.
5. For a criminal situation, look up Drink or Die. For an extreme criminal example, look up Kevin Mitnick (I recommend the book "Takedown" by Mitsomu Shimomura) Also see Dimitry Skylarov. (Both civil and criminal in that case, but both are resolved.)
6. Napster is an extreme example of DMCA on the civil side.
7. Look up "Usher" and "DMCA" on google. There was a professor named Usher at some university that recorded his lectures, and distributed them. He got a DMCA complaint, and responded. From what I know, it stopped there. It could have been a lawsuit in the other direction.
Hope this helps clear some things up.