Meh. At least for the 13" Macbook I have. Viewing angle changes contrast/gamma significantly.
My wife's MacBook, which I calibrated for fun, really really sucks in every respect for image viewing. The screen is obviously built for casual browsing and word processing and fails miserably at viewing colors and viewing angle is minimal.
On the other hand, my Macbook Pro 15" with matte screen (old intel version) is almost as good as my very nice Samsung 23" monitor. The ONLY difference I see between the two is that the MBPro has a very very slight salmon color cast compared to the Samsung even after calibrating.
On the other hand, the MBPro has LED screen so its colors and luminosity is good at startup. The Samsung takes about 20 min to warm up.
For me, having the size of the desktop monitor is nice but I would never wait till I got home because of calibration concerns. If nothing else, you can do 99% of the work on your laptop (assuming its a decent screen like the MBPro LCD matte screen) and then just check at home and tweak if necessary.