Hey mate, due to this not being Gnu/Linux related, you've posted this in the wrong forum. It should have been post in the, 'Other *NIX' forum.
I have never used macports but i did look into them a while back. To my understanding, mac ports work just like Gentoos emerge. This means if you use it, it will compile all the software that you install. If you rely on battery, and can't get access to a powerpoint then it may not be a good option, if you intend on a large piece of software, like kde. This is because compiling something like that will use a lot of cpu and drain you battery faster. Another thing you might want to look into as an alternative is installing 'apt' on your mac. This should work very similar except it'll install per-compiled binarys (packages) instead of compiling on your own machine. It'll be faster, and take up less resources.
Unfortunately i have zero experience with either of these programs on mac, so i can't give you any more info, but you'll turn up heaps of helpful info you google it.