I can't seem to get a straight answer on this at all. And like pretty much every trendy/newly-invented-word*, everyone has their own definition.
When I first started to hear/read the word foodie I was like, "ok, these are people who really like food..." But seriously folks, who doesn't like food? So is there a higher degree of like-age here or something???
Then I started to hear that it's basically the same thing as a "gourmet" - but that people think that gourmet = snobby, so they made up foodie to imply something more down-to-earth.
Digging further I found that a lot of people HATE the term foodie AND think that it implies plenty of snobby-ness (I came to this conclusion after reading far too many message boards discussing the definition of "foodie" - made my head hurt honestly). It seems that these "foodies" get obsessed with reading up on every new restaurant, going there and critiquing their dishes based on whatever article/book/blog they just read (these readings generally telling them what the new trends are for ingredient pairings and which newly discovered wines go best with them). Some of the foodies actually get into actually cooking things themselves in order to substantiate their expert knowledge of food.
This description of foodies kind of reminds me of those "sports fans" who get all their information from Sports Center and PTI and proceed to repeat the opinions of these television personalities instead of actually watching the games and coming up with their own opinions.
I'm definitely not pretending to be better than these types of people AT ALL. With my constant moving around for the past two years, I've done a piss-poor job at keeping up with my favorite sports teams. Sometimes I like to pretend I'm still a dedicated fan, but I will quickly admit that I know nothing these days about the players, stats or what-have-you. And since I'm just getting into this whole cooking/culinary thing, I know I have plenty to learn - and I will read articles and books about food in order to do that.
I guess my conclusion here is that I still don't know what a foodie is and so I will never call myself one. I'm not an expert on food or cooking and even as I learn more I will take everything with a grain of salt (BAM! food idiom!) and try my very best to stay true to my personal taste.
* according to my research, the term "foodie" was coined in 1981. So maybe no-so-new. Depends - like always - on your perspective.