I understand it insofar as it means that a device is altered in some way that allows other types of software to be run on it. What I don't get is who would do such a thing, and why.
(No offence intended here, honest)
I can see that nerds and computer geeks would want to play around with the OS to see if they can make it do things that Apple never thought of or which they thought of but decided against for one reason or another. I think it's great that there are guys out there with the skill and knowledge base to be able to do things like make a new keyboard layout work or any of the other things that jail-breaking allows. What I don't get is why Joe Public would take that info and apply it to his/her own iPad, iPad2 or any other device that Jail-breaking works on.
My iPad 2, with accessories bought at the same time, cost me about £520 and it is now almost a year old. I love it to bits. Before I bought it I did a lot of research as to what it would do and what it wouldn't so I knew exactly what I was buying. Would I mess around with the internal stuff? No way, Jose. I understand that there is a way of deleting the jail-breaking so that your warranty is not voided by the Apple store but do I want to take the risk of my iPad breaking down and being unusable and therefore not able to take it back to an un jail-broken state? ... Not really.
Put it this way, if I spent £20,000 buying a new Ford Mondeo, would I take it home and rip out the computer and insert one from a Vauxhall just so I could get a HUD? No, I'd buy the Vauxhall in the first place.
I ain't dissing folk that HAVE jail-broken their iPad2. I hope you enjoy the changes. I think what it is is that having had to pay for my iPad 2 out of my own pocket I want to keep it working for as long as possible. Maybe if I started off by buying an "iPad 1" 3 or 4 years ago and was now looking at the idea of buying an iPad 3, I would look seriously into jail-breaking the iPad 1, mostly because I had got my money's worth out of it and jail-breaking it may negate the need to buy the iPad 3, at least for a while.
Like I said, just asking and not meaning any offence to anybody.