I have been a Scout user for a while now. I primarily use it for its Rails monitoring. They also have a Passenger plugin that monitors a number of Passenger stats. My setup doesn't lend itself to Apache log monitoring (which is what the article refers to).

As a monitoring app, I have no complaints but also have little to compare it to. It's worth a look and hard to beat on price, in my opinion. I'm not someone who would roll his own monitoring system so it works well for me.