Whenever I try to run adb devices
:
$ adb devices
* daemon not running. starting it now *
* daemon started su
I uninstalled Dell PC Suite and HTC Sync from my computer and this problem went away.
EDIT: To elaborate a bit on the cause of this problem: HTC sync comes with an ADB server of its own. And it updates your PATH environment variable to point to its version of the server. Edit the PATH variable and remove the reference to the HTC Sync directories. Now you're using Google's ADB again.