I think a lot of people are now reviewing their personal and corporate email policies, especially people who use cloud-based email on work computers. The mainstream, non-tech press, has spent some time trying to explain this, too; I saw a segment on the CBS Morning News yesterday that did a decent job of it, although they didn't get into too much depth. The best comparison their expert used was that email is like a postcard. I'd say it's like a telegram, a telegram that never disappears and is searchable. 

Please don't take this wrong not meaning to be political but realistic

No matter what you put to [e-mail] you must remember you must write that not only people reading with good intentions can understand you must also write so that people reading with bad intentions cannot misunderstand.

That which is not secure and can be read by anyone.  That which is to be considered to be totally secure is probably not and refer to part one.

I think it is quite apparent about the security issue and transferring data is always a bad thing.

Anytime you oppose, cross or otherwise dispute or intimidate people in power you will find that someone can find whatever they wish about you. 

I see the cloud with some apprehension in the same manner, but guess I am just old fashion.

>>then as long as your door is locked you're probably okay<<

That probability should be carefully looked at. And shouldnt cloud users begin to  worry about numbers of duplicate keys in different hands when the assumption of getting your door locked and contents secured?

I had no idea the age of a communication was relevant to whether a warrant is needed to obtain it.  Strange.

Despite earlier reports, it was not Gmail headers. Rather, it was Petreaus' mail client, reported Digital Trends. According to my understanding of the case and the law, the FBI must have got a warrant. They need one to access emails that are 180 or fewer days old. To gain access to older emails, however, they don't need to show probably cause... something to ponder before clicking send. Here's the User's Guide to the Stored Communications Act.

The thinking is that by having an affair, Petreaus left himself open to blackmail. If he was having the affair while in the Armed Forces, he broke a military law, which is one reason it's been reported he said the affair began after he left the service. It also could be argued it distracted him from his duties, and it puts his moral character into question. As head of the CIA, the fact that he was doing something illicit is dangerous to the nation because, if discovered by an enemy country, that nation could have held it over Petreaus' head, arguable. (I disagree, really: He fessed up immediately, it appears, rather than argue over it or disavow it, only to have the truth come out after a protracted PR nightmare. But you can't know how an individual will react.)

I'm uncertain whether this "Gmail metadata" was in fact Gmail-specific, or whether it was simply ordinary email headers. 

NBC Nightly News reported Monday night that the FBI investigated started (as this blog notes) with an investigation into threatening emails sent to Jill Kelley. Investigators became alarmed when the person sending the threats appeared to have intimate knowledge of Gen. Petreaus's locations. Investigators accessed the account sending the threats and discovered sexually explicit email that was evidence of the affair. 

Do we know how the investigators accessed the account? Was it definitely through a warrant served on the ISP? Was the ISP in this case Google?

@Alison Diana: Okay help me with the thought on the security scenario. lets say some one wanted Patreous  or Mrs. Broadwell that bad, how would they have orchestrated either of their downfalls had Mrs. Broadwell acted the way she did?

Great points, @abdiah. The FBI was obviously given a big clue and a trail to follow; this wasn't an accidental uncovering after a sweep of Gmail. I guess it's like any security scenario. If someone wants you, they most likely will succeed. But if they're jiggling on door handles, then as long as your door is locked you're probably okay. At least for now.

Yes, email lasts forever but in cases where secondary issues do not compromise them, they may be secret forever as well.

I think another angle to this is that we must note that in life we cannot control everything, no matter how careful we think we are. This is a case of quite secure communication plan being accidentally compromised.