I'm using an outputlookup to generate a list of services for which alerts have been raised in the last 60 minutes. I'm then using this to suppress alerts for the same service within that hour. This works as long as I have a steady stream of different alerts. If I have a lengthy period without any alerts the last alert that I have is suppressed indefinitely.
The problem is that if the search feeding outputlookup doesn't generate any results then the outputlookup doesn't overwrite the file. This means that I never end up with an empty file and consequently I suppress results I shouldn't be.
I'm using this mechanism to suppress the alerts because I want to suppress duplicates for specific events within a given time period and I don't want to define searches for each of the 100+ events I want to trigger a specific alert about. If I could suppress results based on a field value in the result rather than the name of the alert I'd do that.