This app is great. I've been using it now for about a week. I have it monitor a mix of intranet and internet servers with no issue and little overhead. There are two features that this app needs:
1. The ability to disable to dock icon. Something like this, where all your interaction is via a menu bar icon and Growl, and doesn't need a dock icon always open.
2. The ability to customize the Growl notification on a per server basis. This is a small shortcoming, but it would still be nice to have the option.
Other than the above, the app works as you'd expect. It's worth the money.