I installed the Lotus Connections plugin successfully.
I could add it to a job config as a post build task, but when I saved the config I got the following stacktrace:
{{javax.servlet.ServletException: java.lang.RuntimeException: Failed to serialize hudson.model.Project#publishers for class hudson.model.FreeStyleProject
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:796)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:249)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)}}
See full stack trace in AddLotusConnectionsPluginStackTrace.txt.

But the post build task remains and you are able to run the job. Running the job with the plugin added produces the following in the console output:
{{Performing Lotus Connections Magic
url = https://w3-connections.ibm.com/
user = [USER_EMAIL]
ERROR: Publisher 'Lotus Connections Notifications' aborted due to exception:
java.lang.NoSuchMethodError: hudson/model/AbstractBuild.getAggregatedTestResultAction()Lhudson/tasks/test/AggregatedTestResultAction;
at com.ibm.ConnectionsPlugin.createForumTitle(ConnectionsPlugin.java:136)
at com.ibm.ConnectionsPlugin.perform(ConnectionsPlugin.java:94)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:45)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:779)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:726)
at hudson.model.Build$BuildExecution.post2(Build.java:185)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:671)
at hudson.model.Run.execute(Run.java:1766)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
at hudson.model.ResourceController.execute(ResourceController.java:98)
at hudson.model.Executor.run(Executor.java:381)}}

Finally, when you enter the config, delete the Lotus Connections post build task and try to save the config you get a similar but not identical stack trace to when you add the plugin to a job: see RemoveLotusConnectionsPlugStackTrace