Jaiku is down, and according to jaikuinvites, it's because they have finally moved their system to the Google App Engine platform. There's no official word from Google about what's happening, but their website describes it as "server maintenance".
If you're wondering what Jaiku is, you can basically think of it as Twitter, but owned and operated by Google. Here's how they describe themselves:
Jaiku's main goal is to bring people closer together by enabling them to share their activity streams. An activity stream is a log of everyday things as they happen: your status messages, recommendations, events you're attending, photos you've taken - anything you post directly to Jaiku or add using Web feeds. We offer a way to connect with the people you care about by sharing your activities with them on the Web, IM, and SMS - as well as through a slew of cool third-party applications built by other developers using our API.
It didn't take long after the acquisition for people to start wondering if Google had forgotten about this service. Twitter has been plagued with downtime, and it is surprising that Google hasn't yet taken advantage of that situation.
We're not too far away from seeing a new Jaiku though -- or at least a Jaiku that's hosted on Google App Engine. Even if the service hasn't changed, it is certain to be very reliable and scalable now that Google is finally hosting it. For proof that it's now hosted by Google, check out the traceroute.