Depends how serious you want to take it, a mac book will let you have as many calibrations as you want, e.g. full brightness, or one notch down, two notches down etc. (I have 3 or 4 that I use). Ambient light is more problematic, if your always working at the same few locations e.g. home and office you can calibrate for those separately.
I use my MBP to edit and once calibrated the screen holds calibration extremely well, and you can edit most photo's no problem, funnily enough the hardest thing i find to judge like you is brightness, if possible I use my separate calibrated monitor...its a much better. With my mbp I often find myself using the histogram rather than the screen to judge exposure, which is obviously not ideal.