The morse code on the Survivor 2299 site (which was registered by Zenimax,
and is almost certainly counting down to the Spike VGA's reveal trailer for Fallout 4 edit: It seems I got the date of the Spike VGA's incorrect, so that isn't what it's counting down to.) has changed now from the date 11-12-13 (which is weird, because it's an American company making a game presumably set in America, yet they're using a non-American date format of DD-MM-YY), to a series of letters transmitted in Morse code.
"ZL QRNE FVFGRE. V'Z URNQVAT GB GUR VAFGVGHGR. TBQ XABJF JUNG UNCCRARQ GB GUVF CYNPR ABJ. GUVF BYQ ONFGNEQ JVYY URYC HF. UR ZHFG URYC HF. —0321—"
Once these letters were deciphered (using a Caesar cipher, apparently, I don't know if that's relevant) they translated to:
"MY DEAR SISTER. I'M HEADING TO THE INSTITUTE. GOD KNOWS WHAT HAPPENED TO THIS PLACE NOW. THIS OLD BASTARD WILL HELP US. HE MUST HELP US. —0321—"
In case you don't remember, The Institute is a location which has been mentioned before within the Fallout series, both in Fallout: New Vegas, and Fallout 3 (where I suspect it was introduced specifically to follow up on this time around).
The Institute lies within the Commonwealth, which, pre-war, was known as Massachusetts. The Institute itself has been around since before the war, at which point is was know by the name "Massachusetts Institute of Technology." Robert House attended there in the Fallout lore, apparently.
The Commonwealth, from what we know of it so far, has been portrayed as one of the harshest areas in the world, even by Fallout standards. Irradiated, destroyed, ravaged by raiders and various factions vying for control, it's a brutal place. The one exception to this, however, is The Institute, which is under strict martial law, and which uses sentient, true A.I. androids as slave labor, but which is nonetheless safe for those who are able to get into it.
The Institute was mentioned in Fallout 3 during the quest "The Replicated Man," as a scientist from the Institute, Doctor Zimmer, and his bodyguard hired the Lone Wanderer to track down an escaped android for them. During this quest the Lone Wanderer encountered a member of another faction who had come from the Commonwealth, Victoria Watts. Watts was a member of "The Railroad," who, inspired by the real-life underground railroad, smuggled enslaved androids away from the controls of their masters, to safety.
So here's what we can gather so far. Survivor 2299, which is most likely Fallout 4, will almost certainly take place in the Commonwealth, among the wreckage of Boston and the surrounding areas, and will likely feature heavily both the Institute and the Railroad within its main storyline (if I had to guess you'll probably be able to choose which to side with, but that's my own inference, no more). The player character will also probably be referred to as "The Survivor," likely after "surviving" some sort of catastrophe during the game's prologue (I'm taking bets on whether the disaster will be set in a vault, my money is on "yes"), and the game will be set in 2299, 18 years after Fallout: New Vegas (which, itself, was set four years after Fallout 3).
Also of note is that it seems Three Dog will have found himself in the Commonwealth by the start of Fallout 4, as the actor confirmed almost a year ago that he's been doing voice acting for the new game.
So, Survivor 2299. ALL ABOARD THE HYPE TRAIN! CHOO-CHOO!
Edit: There was also a "leak" this past Spring where a supposed Bethesda employee let the internet know that Fallout 4 would be set in Boston... I hesitate to even mention it though, because the whole thing was super sketchy, and the smart money has been on Fallout 4 being set in Boston literally since The Commonwealth was introduced in Fallout 3.