I just noticed that I have a 2MB ~ file in the root of my Macbook HD. This wasn't here last time I checked (probably months ago,) and my guess is that it is from a system crash the other day or maybe from the upgrade to Yosemite.
What is this file and can I delete it without incident?
This seems to be an attempt to write something to the ~ directory, but instead has been written to the file /~. This file isn't required by OS X, but if an app is still using it then deleting it could break things. Make a backup if you delete it.