I applied through Slough Nationality Checking Service on 30th November 2006. The Slough Nationality Checking Service sent my documents via special delivery to Home Office. Royal mail website tracking service confirms that they were delivered to Home Office on 2nd December 2006. I have still not received any acknowledgement from Home Office. Can I travel outside UK before I recieve official confirmation (as one of the conditions is that one must be in country when Home Office receives nationality application)?  

If, as you say "Royal mail website tracking service confirms that they were delivered to Home Office on 2nd December 2006" I hardly think you need wait for an acknowledgement.... You have got proof that the Home Office have received the application.

paul