1. A service model impact propagation method, comprising: creating a data structure of a service impact model, the data structure having nodes representing components of the service impact model and having impact relationships between at least some of the nodes, each of the nodes having one of at least two states; associating counts with at least some of the nodes, the count for a given one of the nodes tracking at least one of the two states for the nodes having impact relationships with the given node; changing the state of a first of the nodes; propagating impact of the change to the counts associated with one or more second of nodes having impact relationships with the first node; and determining the state of the one or more second nodes with the counts.