Or Mac, or "Cloud Reader" through your web browser.

+1 for cloud reader for programming books. It's open in one window, code in another, terminal in another. Drawbacks, however, include (1) is you can't copy-and-paste from the book; and (2) links don't work [which makes drawback (1) very annoying].

Android as well.

Amazon provides also a chrome plugin for PC

There's also a client for the Blackberry.

It sucks, but it'll do in a pinch.

How do I download the book so I can read it on my iDevice?

Officially, you need to use the Kindle app.

Unofficially, it's easy to use Calibre to convert them to epub. (DRM add a few minutes of extra work.)

The official version of Calibre doesn't support stripping the DRM out of the file, does it?

That's right. I only use Calibre for converting. I use the Python scripts from here [1] to remove DRM. The newer versions have GUIs; they should be friendly enough for most readers here.

[1]: http://apprenticealf.wordpress.com/2010/02/11/hello-world/

And on Linux?