We are very fond of the flexibility it offers in terms of setting up our builds. We have a wide variety of components we need to build which often require custom actions or manipulations using in house technology. Bamboo allows us to set this up quite easily by the flexible configuration features it includes.
Secondly we really like the integration of the build aspect and deploy aspect. One of the recent major releases included this feature to link build and deploy projects together allowing a deployment pipe-line to be setup completely in Bamboo. This makes the status of deployments very visible and also allows for easy follow up and even rollback in case a deployment causes too much havoc.