I bought v1.5 quite a long time ago, and have found it to be a great graphics tool for my use. I'm not a graphic designer, so I cannot justify the cost of Photoshop. But, occasionally I do need to open or edit PSD files generated by a real designer. Acorn has worked well for doing this. The other app that I use for this is Pixelmator, it's a toss up between the two for which is better. But, I prefer Acorn slightly, because it is easier for me to use.
I didn't upgrade to v2.0, because v1.5 was good enough for my needs. But, now that 3.0 was released, I bought it in the App Store. 1.5 was getting a bit dated, and I ran into more than my share of crashes with it. So, I'm hoping 3.0 is more stable, and the UI looks more polished and capable in v3.0.
Note that owners of previous versions can upgrade for $20 (I think that also applies to v1.5). But, I just bought it for $30 in the App Store, because I prefer to manage all my purchases/updates in one place.