Sorry for the late reply... This has been a trend for a bit now. Designer news switched their logo and icons over a while ago - that's the first I saw it. I personally avoid using trends at all costs because they will quickly look outdated. Instead I try to see what I like about it or others like about it and use that information to improve upon my designs. Unless I want to be constantly updating a design or website for someone, using trends in your own design is usually a bad idea. I do using subtle long shadows work well with flat or minimalist design, as long as it is subtle. It simply gives a bit of dimension and can make certain elements pop. A site I did a couple months ago has long shadows on the icons and I think it looks alright. Better than just plain old icons. I've also found that greens and blues tend to work best - yellows and oranges look worst.