Mac Rumors writes Apple is planning to debut a sub-notebook at MacWorld that will feature an external optical drive. There's also a rumour that Apple is going to unveil a notebook with a multi-touch trackpad.
A Mac sub-notebook is indeed expected to be coming at the Macworld and, as rumored, will not coming with an internal optical drive. This omission is presumably due to Apple's ongoing efforts to reduce the size of their laptops. Instead, Apple is said to be offering an external optical drive with the sub-notebook. This detachable external drive would allow customers to read/write from CDs or DVDs as usual, but would allow users to leave this extra bulk at home when on the road.
Apple is also said to be introducing more than one notebook revision at Macworld. What combination of Sub-Notebook, MacBook or MacBook Pro remains unknown, but we've heard that at least one of these new notebooks will incorporate a multi-touch trackpad. The possibility of a multi-touch trackpad has been suggested by both rumors and published patent applications but has not previously been explicitly confirmed.