Yes it is. There are a lot of aspects of editing through photoshop that are very artistic and require a good eye for colour, light, etc. just like any other art. Plus I know a lot of people who use photoshop as a primary tool for drawing/painting using a tablet so it can be used as a digital extension of a traditional art form
I do. I'd label it under digital media. It's especially art, considering there are different levels of photoshop that can be done. I've seen some really professional work, and I've seen some quite shoddy stuff.
Like all art, it takes finness, creativity, and an eye for it. Even if it is someone is creating simply manipulation of a pre-existing art piece/photo, I'd still call it art. It'd be just like the Campbell soup can art by Warhol then.