I’ve been reading the comics for about 5 years, I’d say.  I always buy the volumes as soon as they come out.  The show was pretty similar at first, but diverged.  Partly I think due to necessity to condense the plot, but also for some TV gimmicks for ratings.  I don’t like it as much as the print.
That being said, I still enjoy it.  It’s a fairly good representation of the comics.  Certain things I haven’t liked about it, but I don’t complain too much.
The only other thing I think will be an issue possibly is the series catching up to the comics and having to make its own ending.  Many people don’t like it, although I find it interesting.  Some of my favorite shows have done that (2 mangas I can think of - Gantz and Full Metal Alchemist), and I like seeing the interpretation as an alternate ending.
Pretty sure one of my other favorite shows - Game of Thrones - will run into the same problem, but I’ve heard they’ve been told the ending to come in the next 2 books already to make the series compatible.
@ryguy:
I fully admit that I am too scared to watch that show.  Zombies scare the crap out of me so screw that.  I’ll stick to re-watching Lost.
It’s fairly tame when it comes to the zombies as far as “surprises”.  It’s pretty graphic, but I don’t find it scary.