I use an iBook at almost every show I record, with a MOTU traveler...It stays very protected in my Gator Studio 2 Go. But I can't stress this enough when using a laptop as your primary recorder.....always run backup. Also, partition your drive, and install your OS on each. Keep one only for taping, and only startup from it when you are. I also always have a HiMD rolling backup just in case.
Battery is a top concern. I always power the traveler off an SLA to reduce drain on the lappy. Running 4 preamps with 48v phantom can run it's toll pretty quickly. I get about 50% more usage when powering off (not on) the bus. About 3 hours. Plus I managed to get 2 additional internal batteries for the iBook pretty cheap...I believe this is the best cost/time/size ratio ... external batteries are scary and I won't use them. All of them risk running at low voltage and putting the iBook into a lowpower mode, which cuts off power and communication to the USB and Firewire port, and shuts off the screen backlight, and is a pain to restart from. It would be nice if it switched right to internal battery, but this will only happen if using a DC to AC inverter. The iGo DC to DC converter (and I presume others like it), that takes 12volts from an external battery and converts it to the 24 needed by the iBook, has caused me tons of problems by triggering the low power mode (a 7ahr sla, only lasted about 1.5 hours before causing the lowpower shutdown). So I just run off the internals and I have about 9 hours with my 3. If I need to change internal batteries quickly, I just hook the computer up to an external using the inverter which is safer, and I have time to change. That rarely happens anyway. I have been known to lug my RV's deep cycle with me on a long festival run, so as not to bother myself with the worries of battery life (ehem10KLFehem). Sometimes wheels are a taper's best friend
Most of this doesn't apply to you yet due to current lack of external powering options for the macbook. Although iGo has announced they're coming out with the proper connector soon, so be warned. Plus I compared battery life between the converter and inverter and the inverter actually lasted slightly longer, and that with no worry of lowpower shutdown.