I purchased a Sirrus for my girlfriend, who recently began her graduate program. This is her first nice bike, and she is really happy with it.
I mostly ride flat-bar road bikes and bought her the Sirrus because it is one of the few real flat-bar's at that price point. After a few test rides on it, I think it compares well to my current ride, a Giant FCR 1. The weight difference isn't that great between the two, and I really liked the way it road. The crank is nice and stiff, and the geometry is aggressive (which is my qualm with a lot of bikes in this price range). I wish they had included a nicer rear derailler, but that not withstanding it is a really nice scoot.
My qualm with bikes in this price range is that they are usually designed to be comfortable, not fast. The Sirrus is designed to do to move. For $500, I would say you are getting 90% the performance of my FCR 1. That's my two cents.