This MacWorld article about yesterday's MacBook Pro announcement mentions something that I think most of the media coverage has missed:
There is one significant difference between the MultiTouch capabilities
on the MacBook Air and the new MacBook Pro models. While the Air
features a larger trackpad, the revamped MacBook Pro line-up retains
the existing trackpad size.
The question of touchpad size and how it affects the usabilty of multitouch gestures is a good one. When these gestures start showing up in PC designs the differences may become more apparent. The MacBook Pro's trackpad is already larger than many PC touchpads so I don't think Apple has much to worry about, but some of today's PC touchpads may not give people with large hands enough space to do pinch gestures, for example. The implications of size for scrolling and swipe gestures aren't as obvious. I'm involved in researching these issues and hope to report more here in the future.