PaeloBird (in her success story) talked at length about how she realised calories count. There was a post a couple of weeks ago where another poster talked about how she realised the same thing. This isn't exactly a new premise on this forum.
Obviously eating more calories than you consume will make you put on weight, but it's also more complex than that. There are different kinds of weight to gain.
The kind of food you eat will effect the kind of weight you put on - whether it's fat, retained water, or muscle. This is a new area, and I don't think much research has been done in it.
I've been doing research on an already-lean Paleo guy who has been tracking his calories / fat intake rigorously, whilst getting his bloods / weight checked on regular basis. After 28 days on a really high fat diet (VLC, lots of meat, eggs, Greek Yogurt, and nuts) he had lost .8Kg but his jeans were hanging off him. They measured his body fat, and realised he had dropped more than 1%, and had gained muscle (they hooked him up to a special machine to measure this). He was doing a total of 7 mins exercise a week.
So basically, of course you'll get fat if you overeat all the time, but if you gorge on high protein, high fat foods, you're more likely to put on muscle (to a certain point).