So a few days ago, Portal was updated with a new achievement, which also implemented a bunch of new items all around in the game, in each map specifically. Radios. They play a morse code audio track.
There are 26 tracks all in all, and some kind of method known as SSTV, people have been able to extract pictures from the audio tracks.

Here they are:






















Now, all the pictures from the first to the twenty second, people have been able to get letters and numbers from, that present an MD5 hash, which subsequently was translated into a landline number in Kirkland, US. This landline you can connect to with one of those old dial-up modems, and from there open a Bulletin Board System session, a kind of communication system used back in the old days. If you can authenticate yourself with the system with the correct username and password, which were recovered from some of the morse code mentioned earlier, the BBS terminal will put out a lot of ASCII pictures. You can see those on these links, pretty huge stuff:

http://img.photobucket.com/albums/v2..._human_bbs.png
http://img.photobucket.com/albums/v2...tation_bbs.png
http://img.photobucket.com/albums/v2...hamber_bbs.png
http://img.photobucket.com/albums/v2...pports_bbs.png
http://img.photobucket.com/albums/v2...om3_inc_bb.png

This is the biggest picture that was extracted, and it is most likely concept art from Portal 2:

http://farm3.static.flickr.com/2801/...b95fd393_o.jpg
A noise reduction filter has been applied, and without the filter, you can see some text, which is just weird memos from the owner of Aperture Science, Cave Johnson. Stuff about witchcraft among other things. I can't track down this version right now.
edit: here it is actually!
http://img63.imageshack.us/img63/930...sciilarge2.png

So far people have hit a roadblock, and can't really extract more information. The BBS terminal is putting out new pictures all the time, but it doesn't seem too relevant to the entire thing.

I can credit all this to the Steam forums btw. where I believe most of this was figured out. There is also a SomethingAwful discussion going on, and they are probably trying to make some break throughs, most likely keeping quiet about it until they get something concrete.