One of the things that I would like to see in Coda is to have a search and replace within the selected text. As a developer, in can be helpful sometimes to have a method to only perform a search and replace within a block of code, rather than a whole file.
I am really digging Coda - especially for a 1.0 app, but one oversight (IMO) is a site-wide find and replace. I have purchased Coda but I really wish I didn't have to switch to another tool to do this routine task.
I really love Coda and I'd love to replace TextMate as much as possible.
I work a lot with XML files that happen to have no line separators ; when I try to open these inTextMate, it just keeps hanging in a loop and processes itself to death. Coda handles this situation much better: no crash, no hanging, it just switches off Syntax Highlighting. I absolutely appreciate that kind of intelligence - it makes software feel more human and less stupid.
Also, I love how replacing text in large documents like these is done with an event loop; Coda doesn't just hang-and-replace, I can actually cancel the replace. Very well done, really - I have a lot of respect for that!