First, there is this text appended to the end of image:
TIBERIVS CLAVDIVS CAESAR says "lxxt>33m2mqkyv2gsq3q=w]O2ntk"

Decrypt this with a Caesar cipher, and you get:
http://i.imgur.com/m9sYK.jpg

This image of a decoy contains the words "out" and "guess", a reference to the steganography software OutGuess:
http://www.outguess.org/

Decrypting the message with Outguess gives you this text:
http://pastebin.com/aXYZzzcv

There is a book code and a link to a Reddit page:
http://www.reddit.com/r/a2e7j6ic78h0j/

Of note are two images ("Welcome" and "Problems?") on the Reddit page which also contain Outguess messages:
http://pastebin.com/sJiGQEPM
http://pastebin.com/2xkvnPER

The text from the Reddit page is here:
http://pastebin.com/RcjRf6sv
but more text continues to be added.
Note that there is supposed to be a double space between one sentence and the next.

The title of the Reddit page:
a2e7j6ic78h0j7eiejd0120
and the Mayan numbers on top (although the Mayan numerals only give the first 13 characters) are two representations of the following sequence of numbers:
10, 2, 14, 7, 19, 6, 18, 12, 7, 8, 17, 0, 19, 7, 14, 18, 14, 19, 13, 0, 1, 2, 0

Subtract these numbers from the text as follows:
U - 10 = K
k - 2 = i
b - 14 = n
n - 7 = g

A full decoding is available at:
http://pastebin.com/iiiAWyNQ

In the book code, 1:20 means to take the 20th character from the 1st line.  There are only 69 out of 76 lines posted so far, but what we have right now is (? = character not available yet):
Call us at us tele phone numBer two one four three nine oh nine six o???????

The full telephone number is (214) 390-9608.  If you call this number you will hear the following from a computer-generated voice:
"Very good.  You have done well.  There are three prime numbers associated with the original final.jpg image.  3301 is one of them.  You will have to find the other two.  Multiply all three of these numbers together and add a .com to find the next step.  Good luck.  Goodbye."

The two other numbers are 509 and 503, the width and height of the image.  Multiplying them together gives you the number:

In addition, you can obtain this number if you look up the PGP key from the "Welcome" message:
http://pgp.mit.edu:11371/pks/lookup?search=0x7A35090F&op=index
where the User ID is listed as:
Cicada 3301 (845145127)

So we are led to the website:
http://845145127.com/
which displays a cicada and a countdown.  The cicada image also contains an OutGuess message, signed by the same key:
http://pastebin.com/L0i40NA0

So we are being asked to wait until:
17:00 on Monday, 9 January 2012 UTC
when the next clue will be posted.

Mon. Jan. 9:
The countdown is up and is replaced by a list of coordinates:

Find our symbol at the location nearest you:
52.216802,	21.018334
48.85057059876962,	 2.406892329454422
48.85030144151387,	 2.407538741827011
47.664196,	 -122.313301
47.637520,	 -122.346277
47.622993,	 -122.312576
37.577070,	 126.813122
37.5196666666667,	 126.995
36.0665472222222,	 -94.1726416666667
33.966808,	 -117.650488
29.909098706850486	 -89.99312818050384
25.684702,	 -80.441289
21.584069,	 -158.104211
-33.90281,	 151.18421

Copy/paste the pairs in Google maps. Is anyone close to any of these locations? Looks like you're hunting for the image of a cicada.