I started a new trunk image yesterday and loaded all the updates, and ever since Object>>yourself does not exist anymore.
On looking a little closer it became:

yourhõ¸
    "Answer self."
    ^self

According to Monticello I haven't modified the Kernel package. The method history shows only one version (md 5/16/2006 ...) and the method name in the version browser is indeed yourself (see yourhoz.png). Using 'revert' actually installs yourself, but I still have the yourh... method.

I just realized that copy and paste didn't work properly, see yourself.png for the system browser output.

The implications of this are a bit worrisome ...
Markus