I don't have the pedigree that a lot of Mac geeks have for typography. I'm pretty sure John Gruber has more typeface related knowledge in his pinky than I do in my entire body. Nevertheless, I do get the benefit of using a monospaced font. I find monospaced fonts making writing easer, particularly in terms of grammar. There is no silly microspopic dot squished next to a trailing letter for a period. With a monospaced font that period (or comma or quotation mark or tilde or guillemet [yes, I went there]) gets its very own real estate just like any letter. After working in a monospaced font, you'll probably feel the same.
For this purpose, I came across Inconsolata a few years ago. Raph Levien created Inconsolata and relased it for free with donations requested. Raph has since been scooped up by Google's web font team. Smart move Google.
I'm not exactly sure how I found Inconsolata but I'm pretty sure Dan Benjamin had something to do with it. I just noticed this evening that I've now been using Inconsolata for a few years and I am not sick of it. That is saying something.
If you are curious, I usually eventually move words to a proportionally spaced font later in the proofreading process. It's silly but switching the typeface after I'm used to it monospaced helps me find more typos, which is probably hard to believe if you regularly read this site.