Jaiku has found its way back online, now hosted at the Google datacenters, but not within the Google Apps Engine as was rumored. From the official blog post:
We’ve now moved Jaiku to a Google data center. This is something that we’d planned to do anyway, as part of our future transition to Google App Engine.
Jaiku is still running its original engine, however, there are some news, like a new TOS and unlimited invites. I didn’t know they were scarce?