Apparently, Best Buy employees are allowed to purchase game guides early, which is what one of them did. Now he's posting various information from it on gamespot/gamefaqs boardsHere are some totals from the appendicies (did I spell that right?):
42 hollowed out rocks (kind of like the one that was near Megaton that held the sniper rifle)
51 Skill books (less skill books but they add +3 to skills or +4 with Comprehension perk)
213 Skill magazines (these will add +10 to skills but only last a small amount of time, can be longer with Retention perk and get +15 with Comprehension Perk)
42 different Unique Weapons (some only available WITH Wild Wasteland, others only available WITHOUT Wild Wasteland
For the Beastiary there are Bighorners (6 subspecies), Bloatflies are back, Brahmin (4 subspecies), Cazadors (look like giant mosquitos, 3 subspecies), 3 different Centaurs this time around, Coyotes (3 kinds), 8 types of Deathclaws, 8 types of dogs, 10 types of Geckos, 10 types of Ghouls, 3 types of Giant Ants, 3 types of giant Mantises, 4 types of Giant Rats, 2 kinds of Lakelurks, 2 types in Molerats, 4 kinds of Nightstalkers (weird cat looking things, supposedly poisonous), Radroach, 6 types of Radscorpions, 5 types of Sporeplants (no picture available), and 6 kinds of Super Mutants.
As for followers, it is true you can have one humanoid and non-humanoid follower at a time. BUT, if you get to a certain reputation with the NCR you are able to call in for a Ranger or Trooper to assist bringing the total to 3 and if you pay for a bodyguard in Freeside it will bring it up to 4, but that's only while you are in Freeside. Also, when playing on Normal difficulty (non hardcore) your companions do not die, they fall unconscious. Only in Hardcore mode do they die. Companions also cannot use modified weapons but CAN use different ammo types.
10 TRAITS TOTAL (can elaborate later if asked about specific one): Built to Destroy, Fast Shot, Four Eyes, Good Natured, Heavy Handed, Kamikaze, Loose Cannon, Small Frame, Trigger Discipline, and of course, Wild Wasteland.
86 total perks are in there. Most are shared from FO3 some are new. Can't write them down now cuz I see a customer walking towards me now.