The Apple MacBook Air is extremely portable--it's so slim it fits inside a manila envelope. But the portability requires you to sacrifice some expansion and connectivity options:
No PC card slot: You won't be able to slot in a 3.5G Mobile Data PC Card or any other PC Card because it doesn't have a PC Card or ExpressCard slot. All peripherals must be connected via the USB interface.
No Ethernet port: You can't plug an Ethernet cable directly into the MacBook Air. You need to use an Ethernet adapter for USB. If you travel often, it may be a hassle to connect the MacBook Air to the hotel's wired network.
No CD/DVD drive: You need to use an external drive to access CDs and DVDs. The MacBook Air provides a CD/DVD drive-sharing software that allows you to access another PC's CD/DVD drive over the wireless network (with permission of the user at the PC of course). If you're surrounded by strangers who won't share their CD/DVD drives, then you're out of luck.
Only one USB socket: If you need to connect more than one USB device at the same time, you'll need to use a USB hub.
Non-removable battery: You can't swap the battery for another if you run out of power.
So while the MacBook Air is highly portable, you may end up carrying many more peripherals like a 3.5G modem for USB, Ethernet adapter for USB, external CD/DVD drive, USB hub and so on. Think about this before you buy a MacBook Air.
Signing off from Sydney airport, and wishing I had something as portable as a MacBook Air, but without the compromises.