However, I now believe that my search is over and that I have finally found a fully featured, beautifully presented and responsive OS for my MacBook: Netrunner 2014.04 with the KDE desktop environment. Netrunner can be downloaded from here and is free.
Netrunner comes in two variants: the one I have installed is based on Kubuntu. There is also a 'rolling' distro based on Arch. I chose the one based on Kubuntu, because I am familiar with Ubuntu-based configuration tools and the multitude of powerful and easily installable software available in the Ubuntu repositories. I also use Kubuntu on my more modern 8 core desktop machine, so I am familiar with KDE.
I booted my MacBook from the Netrunner DVD, as the creation of a bootable USB key for Mac hardware requires you to jump through many hoops, and have access to a working version of OS X, long formatted out of existence on my machine. Booting from the DVD brings up a live Netrunner environment which allows you to play with the OS, check that your hardware is working, and gives you a feel for the distro before you decide to commit to an installation. The installer is well designed and makes things like disk partitioning very easy for the novice to Linux.
As Apple have decided to make the firmware for the iSight camera (the webcam installed on the MacBook) proprietary, this is the only hardware that does not work 'out of the box' under Linux. This is easily fixed once you have installed the OS to the hard drive and have connected to the internet: simply follow the instructions here to install and load the firmware, and 5 minutes later your webcam will work in Skype and other applications.
bless --device /dev/disk0s1 --setBoot --legacy
(this assumes that the bootloader is on sda1, otherwise /dev/disk0s2 if it's on sda2, etc.)
This will speed up your boot time considerably.
The Netrunner desktop, at first glance, looks like a conventional KDE desktop. KDE has some similarity in terms of desktop layout as pre-Windows 8 versions of the infamous Microsoft operating system, so Windows users making the move to Linux will feel at home here quite quickly. There are some differences to a conventional KDE desktop however. Firstly, the KDE start button and start menu has been replaced by a widget called Homerun Kicker. I was so impressed with the speed and sensible layout of this system, that I immediately installed it on my Kubuntu desktop system as well.
I use the terminal a lot. I prefer to use it to quickly install software, edit configuration files and generally manage files and data. Netrunner comes with a nifty terminal application called Yakuake. It drops down from the top of the screen like the terminal in 'Quake' when it is summoned using the F12 key. Very nifty, very handy for power users. Again, I have installed it on my Kubuntu desktop as it is extremely useful.