JaikuEngine differs from Jaiku in a few key ways. Although core features like the website, SMS (in the US only) and IM bot still work, feed fetching and international SMS are no longer available.
International SMS also had scaling issues, but for financial rather than technical reasons. One potential solution is to use IM on capable mobile devices such as the G1. Developers can also build clients that take advantage of presence and other features of the new JaikuEngine API.
We'll be releasing the open source JaikuEngine code and sharing more information in the coming days. Stay tuned!