What is an appropriate directory in which to install Android SDK?

On Linux, I typically use /usr/local/android-sdk, but anywhere that makes sense and that won't get clobbered by your system works. Just be aware that it may actually make sense to put the SDK in a per-user location, since it requires write access to create a VM image and to download SDK updates.

Common locations are /opt, /srv, and /usr/local. I tend to lean toward /usr/local.

Note that the Android SDK doesn't really require you to install much, it's mostly self-contained. All you need to do is tell Eclipse where it is. You may also want to add the tools and/or platform-tools directories to the system-wide PATH so that your users can use adb and other tools.

See http://developer.android.com/sdk/installing.html.