I had to redesign my portfolio website recently, and as Coda had just been released by Panic, I gave it a try.
Of all the good features this app offers, the best experience I had with it was actually the Panic sans font rendering on the screen. It's sharp, rounded, very comfortable to read. I used to work with Monaco 9pt as I found it was the most lisible font I had to work with code, but Panic sans feels so much better, as you can see :
Working code with an inappropriate font is like sitting at work all day in a bad chair, and Coda's font is like sitting in a sofa for that matter. Of course there are other good aspects such as the easy way to upload files or the one window thing, but this is a little detail making a lot of difference. This font being named from the company who did the software, I guess they did put some work into the rendering of the font at these small sizes.
One con though about the app : having to be online to access the reference book doesn't seem right to me. Sure, web development often means being online, but not always. So yeah, that was a bit of a frustration the first time I tried to look for some information there and that I was said I had to be online to get there. Is this part of the trial's version limitations ? I'll know the answer soon I guess, as I'm considering buying it.