These days, my primary computer is a 15″ MacBook Pro. It’s an amazing machine, but sometimes those 15″ can be a little unwieldy (yes, that’s what she said).
Apple used to make a small, very portable laptop: the 12″ PowerBook, which was unfortunately retired during Apple’s switch to the Intel platform. However, the transition did introduce the potential ability to run Mac OS X natively on non-Apple hardware. Whilst Apple don’t (currently) make their own netbook1, a big community has sprung up around running OS X on non-Apple netbooks. I should note from the outset that installing OS X on non-Apple hardware potentially violates the OS X EULA. If you’re going to do this, in the very least ensure you own a legal copy of Mac OS X Leopard.