With recent correspondence from Thomas Spycher of, He has informed us that they ( have chosen to utilise Icinga for the monitoring (appropriately 500 hosts!) of their server equipment.
Here are some extracts from a recent Blog from Thomas with his thoughts on Icinga, and how he will be implementing it throughout

Original post from: netzwerk-und-server-monitoring-mit-icinga

… Icinga still is quite young but my first tests ran extremely stable. The text-based configuration is more complex but provides a lot of possibilities for automated solutions.
… First Tests were very successful and we are thinking about replacing the current productive monitoring system by icinga. Due to the great flexibility, extensions are set up extremely fast.
… That’s why Genotec doesn’t use just sms and e-mail for notification but also Prowl to push notifications directly to iphones. For documentation of outages, internal tracker items for the internal system are automatically generated. There are endless opportunities. It takes 5 minutes to set up notifications via twitter.
… Contact to the developers of Icinga is great! We and Icinga are looking forward to complete the go-live of our instance and to release the first Icinga stable. Furthermore we are confident about the teamwork with Icinga and we are sure Gentotec and Icinga can benefit from it.
… It looks like Gentoc is the first provider who relies on Icinga. I am confident this direction is the right one and I am looking forward to keep you informed about further steps of this project.

Also I have to add, Thomas informed us via twitter, that he had the released 1.0 RC1 up and running within 10 minutes of the release hitting SourceForge!
So thank you Thomas and for both choosing Icinga for your monitoring solution & for making contact with us. Your feedback is encouraging for the hard working development team who have spent many hours to achieve (what  has been a remarkable job in 5 months!) the first Release Candidate of Icinga…