Several rumors have been going around about the possibilities of an ultraportable Mac. The sub-notebook will supposedly be lacking an optical drive and come with or have the option of an external optical drive. Other rumors of a multitouch trackpad with capabilities like that of the iPhone, with swiping and zooming.
The most interesting rumor, and perhaps the most far-fetched, is that the ultraportable will have a docking station. The docking station will resemble the iMac desktop PC. But this desktop will have a docking station on the side that the ultraportable Mac will simply slide into. This would be like having a desktop PC and an ultraportable notebook in one.
These are still Rumors of an Ultraportable Mac, but I would be surprised if we dont see an ultraportable Mac at Macworld 2008 with all the hype going around.