If you've already got the Macbook then follow the advice given by DZC in the comments:<p><i>"I install a minimal Ubuntu (like JEOS) to a VirtualBox instance on my MacBook. It's set up to be as minimal as possible -- no sound, X, etc. Then I set it up as a local server -- mounting it's file system via SSHFS (or NFS or whatever you like) to the Mac OS side.<p>Then I can use Mac OS Terminal, Textmate, Firefox, etc. for development. The only major downside so far is the ~10% CPU VirtualBox seems to use at idle."</i><p>And if you intend to run Linux, don't buy the Macbook. In fact if you're technical enough to be reading this then you're technical enough to plan to buy a machine that's going to run well under linux (no binary blobs etc.) which isn't, even today, a complete no-brainer.
This is why I sold my MacBook and bought a ThinkPad T500. While it's nice that every single MacBook that is your exact model has the exact same hardware and runs very well on OS X, I have found that Lenovo laptops run better on Linux.