I read the first four books before the TV series had even been heard of. Read book 5 as soon as my local library had it available. I spend hours per week on towerofthehand.com studying all sorts of things that have to do with the storylines of the books AND the TV series.
For the most part , the TV series has been spot on to the books. There are, of course, a few changes... Asha Greyjoy, anyone??? In the books, it is also only hinted at that Renly and Loras might be more than "friends" and Margery is an innocent, still, when with Renly.
Everyone I know despises Joffrey for good reason, and they all really like Tyrion. All in all, the books and TV series earn 5/5 stars from me.
~Tiger