The decision couldn't come soon enough. The ill-conceived electronics ban started back in 1991 when both the FCC and the FAA restricted airplane cellphone use, largely because no one actually knew what a cellphone was, much less how they actually worked. Better safe than sorry. A year later, though, they ran actual tests to see if there there was any valid argument for their blind terror. Surprise! There wasn't.
But facts can be a tricky thing, especially when you decide to completely disregard them. Figuring that an abundance of caution in the face of all contrary evidence was in order, both the FCC and the FAA decided to keep the ban in place because, hey, why not. And this has gone on, totally groundless, for the past 20 years.
There has been, in fact, only one recorded instance in aviation history in which a cellphone proved dangerous; in 2009, a first officer became distracted when his phone rang because he forgot to put it on vibrate. So maybe keep the ban going for that guy. For everyone else, though, you're finally free, thanks in no small part to the repeated protestations of the NYT's Nick Bilton.
Of course, just because airlines now have the OK to save you from ever pausing Candy Crush again doesn't mean all carriers will be able to follow these guidelines right away. They still have to prove to the FAA that their planes will in fact allow safe use of any electronic devices from gate to gate, but the agency expects that most—if not all—carriers will get the go-ahead by the end of the year.
Once airlines do get approved, personal electronic devices such as e-books, handheld games, laptops, etc. will finally be non-contraband, with a few limitations. In cases of low-visibility, for instance, the airline crew might tell passengers to shut off these devices during landing. Additionally, heavier items will have to be safely stowed during takeoff in landing, although this is mostly to avoid a potential concussion as opposed to any potential danger posed by the batteries within.
It is still recommended that you keep your phone in airplane mode. According to an FAA spokesperson, though, there is (as we've all suspected) absolutely no safety problem if it's not; you'll just "arrive at your destination with a dead phone." Because good luck trying to get 4G at 30,000 ft. [FAA]