His ult is lackluster. It's hard to notice if you have it on you. The pet dies way too quickly for you to be revived if you do notice you have it on you. You die too fast if you somehow get revived.
Sig courtesy of GrandmasterD. Go get your own sig from them. :D
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http://www.leagueoflegends.com/board/showthread.php?t=879795 (red post acknowledging bug)
reddit post from someone who experienced it:
http://www.reddit.com/r/leagueoflegends/comments/i6ch5/yorick_is_op_oh_and_glitched/