For example the parameterized-trigger uses Future.get to wait for a triggered build to finish, when a NullpointerException was thrown in the ArtifactDeployer's onDeleted the build that waited was waiting forever.

The exception from the log that caused Future.set to not be called correctly was:

Jul 5, 2012 11:00:24 PM hudson.model.Executor run
SEVERE: Executor threw an exception
java.lang.NullPointerException
at org.jenkinsci.plugins.artifactdeployer.ArtifactDeployerPublisher$DeleteRemoteArtifact.onDeleted(ArtifactDeployerPublisher.java:187)
at org.jenkinsci.plugins.artifactdeployer.ArtifactDeployerPublisher$DeleteRemoteArtifact.onDeleted(ArtifactDeployerPublisher.java:171)
at hudson.model.listeners.RunListener.fireDeleted(RunListener.java:208)
at hudson.model.Run.delete(Run.java:1187)
at hudson.model.AbstractBuild.delete(AbstractBuild.java:362)
at hudson.tasks.LogRotator.perform(LogRotator.java:157)
at hudson.model.Job.logRotate(Job.java:315)
at hudson.model.Run.run(Run.java:1440)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:175)

Although it was due to an exception in a plugin I think the Executor should be a bit more robust in this case.

This mail thread has a similar description of the problem: https://groups.google.com/forum/?fromgroups#!topic/jenkinsci-dev/P7XiYknqgoI