The MacBook Air is long overdue for an update to its hardware, having last been refreshed in June of 2009. Aside from a CPU bump (almost certainly sticking with Core 2 Duo), increase to 4 GB for the base RAM, and an increase in hard drive/SSD capacity, I'd expect to see the glass trackpad make its debut on the MacBook Air as well. Currently, the MacBook Air the only Apple notebook that still has a separate button for the trackpad. I also wouldn't be surprised to see the NVIDIA GeForce 320M replace the previous model's NVIDIA GeForce 9400M, assuming Apple found a way to cram the newer GPU onto the MacBook Air's tiny logic board. One more feature that would be nice, but that I'm not holding my breath for, is a price drop -- since the release of the iPad, the MacBook Air seems like even more of a niche product than it was before.
Several thousand of these units are reportedly on their way to Australia, so you can pretty much bet the farm that you'll be seeing a "Store is Down!" post from us sometime early Tuesday morning.