Andrew Watt, an infopath MVP asked, "What exactly is Acrylic for?"
Acrylic is intended for pro designers (people who use today's pro design tools) to create rich visual content, primarily for use in user interfaces, either desktop apps or web apps, although for the pure artist it's also an excellent tool. It's target audience is not developers or hobbyists or information workers, so these folks may be initially frustrated attempting to use the tool because of their lack of familiarity with this class of tool.
Whether the pro designer primarily uses vector tools or bitmap tools, Acrylic will enable them to create designs combining the best of both.
Acrylic does overlap somewhat with some existing pro designer tools, but I think it is more complementary than anything. If you are an artist, you can use Acrylic, and you'll have a blast just drawing stuff. It's variation palette, among other things, makes this an amazing experience. But the core focus for Acrylic is in areas that are fairly unique, because Acrylic's uber-goal is to help designers become more deeply integrated into the application development process. Acrylic has the ability to output XAML, which can be used as the UI for an application. In todays typical workflow, a designer uses a design tool to prototype the UI, and throws it over a wall to a developer, who attempts to implement the UI in code, but the developer may miss nuances in the design, or it may take too much time to get it just the way the designer wants, and much of the aesthetic appeal of the design can be lost. With Acrylic's XAML export, developers can use the designer's full content in the application interface; no need to attempt to recreate it.