Great application, very useful to reduce the visual noise and improve the focus on the currently selected application. Personally find it very useful for doing my university work and programming, as well as performing browser research without and distractions.
Excellent app! It's saved me hours on distractions. One thing I wish that it had is a blur feature in addition to darkening, but that's a minor gripe and I love it anyways! According to the in-app statistics, it's dimmed windows for me for 250 hours.