When I travel and need to cut weight, I leave the 13" MBP at home and use a Acer Netbook (Linux). It works very well for Internet/email, and as a connection between portable HD for backing up images via USB 2. These weigh about 2 lbs, so you will save about 3 lbs with this switch.
I also put movies on it and use it via the plug-in adapter for in air entertainment. (either that or the iPod for music or smaller screen video.)
There are frequently limits on backing "un-attached" lithium batteries in your check-in luggage too. I've found 2 batteries for the 5D2 to be more than sufficient for travel.
When I've also had to go light, I too have left the macro at home and used a 12/25 mm extension tube with the 70-200/4 IS zoom.
Finally, I've recently "designed" my own hiking backpack for my P65/5D2 equipment (with custom installed zippers, handle and inserts) that weighs in at 3.5 lb---and has an internal frame. It is very comfy with a 30 lb load, and has space for cell phone, water bottles and stuffing jackets, etc. I based it on the Osprey Atmos 35 backpack.