Jaiku is not disappearing completely from the scene. It would have been an another shock for me after demise of Pownce. Here is what Google has to say about it:
While Google will no longer actively develop the Jaiku codebase, the service itself will live on thanks to a dedicated and passionate volunteer team of Googlers.
Many microblogging sites are feeling the heat after higher growth trajectory of Twitter, which has found acceptance even among professionals, like reporters, celebrities, players, etc. It can be said the same about Skype couple of years ago, when many reporters started using it in first in remote areas, then on regular basis. But I personally think that the competition is very important for better services. Well, maybe Jaiku has chosen different path, but it shall amuse loyal microbloggers over the course of time.