I'm obsessed with coming up with the perfect font for long-form writing (for me). Some may say that this, as with my hunt for the perfect color scheme (relatedly, I've been loving Solarized), is not only a pipe dream, but also just another way of procrastinating. They may be right on both points, but that's not going to deter me.
One of the many writing apps I tried on the original iPad was Writer, by Information Architects. The thing that stuck out for me immediately was its font. I of course loved that it was monospaced, but what really pulled me in was its tracking; it just seemed perfect to me, and quite unlike anything else I'd seen on the iPad.
I read somewhere that the font was a customized version of Nitti Light, from Bold Monday, and so a few months ago I did a little digging and found out that the font was available for general purchase, albeit without whatever iPad-specific modifications were made to it. Naturally, I bought it. (It's ~$75.)
It's beautiful on the Mac, and I dare say it's the best font for writing I've found (especially with a medium-contrast, dark-on-light color scheme). However, there is, of course, a problem: it's got ligatures that I can't seem to shake, no matter what I do.
As you can imagine, this is terribly frustrating, because it means that any time I type, e.g., "fi," the sequence is replaced with a ligature that throws everything off balance. As far as I can tell (and I've done a ton of searching), there's no way to disable, system wide, ligatures in Mac OS X. In fact, many apps appear to not respect the "Common Ligatures" checkbox; it doesn't matter if it's checked or unchecked, the ligatures remain in most of the programs I've used. (If they do respect the setting, it seems sporadic at best; I can't make heads or tails of it.)
I wrote the company a few weeks ago and asked if there was a solution. I've yet to hear back from them. If there is no system-wide solution for Mac OS X, surely they can just send me a version of the font that doesn't contain ligatures, right? If not, I'd like my money back, because frankly, it's unusable for me. (Update: They've just sent me a ligature-free version of the font! Now that that issue's been resolved, I can't recommend it highly enough for all you writers out there. Go grab it.)