IMHO ….
Disclaimer: I'm doing something similar http://worqshop.com. The difference is the angle. It's not just a text editor with file transfer (FTP, Dropbox, etc.). I'm doing an IDE for the iPad. With GitHub support (and soon, Heroku deployment).
At the moment, iPad is not very good as a development environment, since Apple doesn't allow you to compile / run code on the iPad directly. You need backend support (e.g. cloud) that allows you to edit / compile / run code on the iPad.
But an iPad with multi touch interface and a bluetooth keyboard opens up a lot of interesting possibilities as an IDE. For example, the multi touch interface allows you to choose colour graphically (see http://twolivesleft.com/Codea/Screen-Colors.png ). Rather than experimenting with different values of RGB, you can just tap it.
I'm still building Worqshop. Thus, I'm not using the iPad as a development tool. I still need Xcode and my Mac :)
At the moment, I'm using Worqshop to edit some HTML/CSS on GitHub, building HTML5 apps with Worqshop + GitHub + StackMob…..
And soon, with Heroku deployment support, I can write Ruby / Python apps on my iPad and deploy it to Heroku.
Footnote 1: I still think the bluetooth keyboard is necessary for fast typing. I can't type very fast with the on screen keyboard
Footnote 2: I still prefer to code using text rather than using graphical items (i.e http://en.wikipedia.org/wiki/Visual_programming_language ). Simply because text is a very compact representation of the semantics of code. As an example, to represent the semantic of "if / then / else" you only need a few lines of code. But with visual programming language, you need a bunch of nodes with graphs, etc. (see http://en.wikipedia.org/wiki/File:Ktechlab_FlowCode.png )