H1-B I-94 form in passport

Long story short. I entered the US on a H1-B as a Canadian citizen and got the I-94 form stapled into my passport with Multiple Entries stamped on it. It's valid until Feb 2013.

However, I recently moved back to Canada for family reasons so have left my US based employment. I still have the I-94 in my passport. What should I do with it?

You were supposed to give it to canada customs when you entered canada (as it says on back of card), but now you should send it to USCIS (isn't there address on the back? -- if there isn't check the website).

You want to have it on record that you left when your quit your H1 job. Your former employer is also supposed to advise USCIS that you are no longer their H1 employee.