Advisor
ProfessorPropertySources generally run only once per day or if triggered manually (I don't think they yet have an execution interval you can define, though I'm told that will be true someday).
However, you can run a WMI query looking for just a specific service as part of the query itself, you don't have to run a full table scan and then examine the results in the code. If you do want to enumerate all services, then you might consider having that one PropertySource generate all the service-based categories you would need. It is not as modular, but is more efficient.
