This thread is fun for me. It was here I first even heard about the series, and the "pre-game" discussion of the book(s), including the "Be careful about getting too attached" warnings.
I went out and bought the first one, mentioned it to my wife, and we started reading it together (well, at different times, but in the same timespan). One of us pulls ahead, then the other passes them when they get busy.
I've also downloaded them through Audible.com to allow me to continue "reading" while driving on a bunch of trips up and down the East Coast I've been making. Not as good as the real thing (reading), but still fun and let's you get your fix.
I'm midway through the third book now, so way ahead of the series, but it's fun to read the comments and see everyone's reaction (the same one I had) when Ned Stark dies. I'll try to keep from mentioning anything not already covered in the show, because so much happens it would be really easy to get spoiled on one plot line or another.
In terms of the army argument, things continue to change throughout the series, but at this point, I still think it's safe to assume the Lannisters have the larger army. Some of Jaime's men almost surely rejoined with Tywin's main force. They also have whatever is garrisoned at King's Landing. I think Tyrion's barbarians are only about 300, though. I feel like the Gold Cloaks are maybe 2 or 3,000, although that's more a guard than a true army.
I, too, loved the fact they killed off Ned Stark. It really brought a lot to the book, and the change of focus on the characters and their reactions was interesting. Martin continues to throw big shake-ups at the reader at least to the point where I am, and one of the things I love about this series is there is very, very little downtime. One of the most frustrating parts about reading it, and probably, soon, watching it, is you get huge cliffhangers, then have to follow a dozen other story lines before the cliffhanger gets resolved. I often skip ahead 6 or 8 chapters in the book to continue one storyline for a chapter or two, then bounce back to catch up on the rest. It actually works, as you have a bunch of mini-stories going on with the occasional interaction.