While checking some of my used plugins I found out now, that in the plugin "serendipity_event_weblogping" (german: Eintraege ankuendigen) there is a service, which is not more available and could now be deleted from the list:
About shut down look here from 28. september 2010:
http://thenextweb.com/ca/2010/09/28/blo ... -to-black/
The domain is available.
Perhaps another service gould be taken out?