I reckon the next iPad anyway so that it's a bit lighter, even though the metal back doesn't account for a huge amount of the weight. Possibly the unibody laptops so that the manufacturing is cheaper and they can bring the prices down a bit. I remember when they switched from plastic to unibody, the prices jumped $100-200.
Getting a $599 Mini again would be nice. $499 would be too much to hope for. Cheaper MBA machines too. Lighter Mac Pros, thinner iMacs and both cheaper etc.
The only concern I have about liquid metal is the colour. I've grown very fond of the shade and style of metal they use currently. Since we'd get lighter, cheaper devices, I'd expect Apple will want to see the return on their investment soon.
The liquid metal sim tool seems to be a darker shade:http://www.iphonehacks.com/images/10...al_SIM_Pin.jpg
I don't know if the menu bar change on Apple's site is significant. It used to be a light grey similar to the colour of the metal they use in the machines and now it's a darker shade like the liquid metal sim tool. I know that's reading into it a bit much though.