It definitely depends on the individual. Not good "nutrition" but I'm the same as Kane. I don't put on fat very easily. And what little I do put on will melt away as soon as I cut down on the olive oil or whatever
I mean, as Widdoes was saying in an earlier thread, I'd much rather be having a steak and potatoes. Much better fuel for gaining. But when it is a numbers game and if a supplement is what you need to bump the numbers, then I don't mind a weight gainer, just like Kane. It obviously should be used to replace an already sound diet. But I think you can see from what Kane and I are saying, we already have a sound diet, we just need a little boost now and again.
It will not automatically pack on fat for everyone. You just have to experiment with it. Most weight gainers are simply made with maltodextrin as the carb. It is high gi. But that doesn't mean it's an automatic fat thing for everyone. The weight gainers that are made with low or medium gi carbs are WAY expensive. Some gainer have added ingredients (certain fibers, fats, casein maybe) to bring down the overall GI of the mix, however. It does have to do with the whole meal, not just one component alone. It is very possible to have a weight gainer with maltodextrin as a high gi carb but have the overall glycemic load of a serving be medium or lower. But there is no guarantee what really happens.