I've been there several times, mainly because I lived in Germany at the time and it was a rare opportunity for me to meet my agents and editors!
It's a huge area and not really suitable for authors, unless you;ve got a special invite, as I had, so I was able to go into the agents' area. The agents all sit around at little tables with lists of their books for sale and talk to the various foreign publishers -- it's a bit like speed-dating, I guess. Everyone is hoping to make the huge deal that will make the headlines so that the publishing world sits up -- I remember the year that The Horse Whisperer sold for a couple million, based only on a few chapters and synopsis (I think that was a movie deal, though). All the professionals are hyper and excited and busy and rushing around -- that's in the first couple days, where the public is not allowed in. The public can visit at the weekend, but by that time the agents and editors have all rushed off home to finalise their deals.
I also went to a big Bertelsman party (now Random House). It was dreadful. Must be thousands of people and everyone knew each other and were talking nineteen to the dozen, and there was poor little me not knowing a soul, and being ignored by everyone. There was however this whole buzz about the place, and it was somehow exciting, knowing that all the big bosses of the publishing world were right there in the room, and maybe some celebrities! But after a while I went to sit down at a table by myself and just watch, and then a woman came and sat down at the table with me, who felt just as lost. It turned out that she was a Hollywood producer, i think with Sony, involved with the Spiderman movies, but she didn't like this kind of affair at all. We chatted for a while and I kind of wondered if I could get her to buy my books for Sony movies, but nothing came of that megadeal!
I wonder which book is going to be the big sensation this year.
Oh. and to answer the OP's specific question: the deals are actually made right there and then, no waiting around and I'll-get-back-to you stuff. There's such a buzz that they don't even read the full mss, I believe. Back then, the agents had short descriptions of the books; I can't imagine they lugged suitcases full of mss with them, yet somehow the deals got done. Once my agent came back from Frankfurt with three foreign sales for me.
I suspect that these days they have the mss on Kindles or whatever. God bless the e-age!