VC Fred Wilson has a nice post on the topic of handing over to a professional CEO.
..there's a good way to do this and a bad way. The bad way is to do a search, find someone you don't know, immediately hand over the keys to the car, and step aside.Arun Natarajan is the Founder of Venture Intelligence India, which tracks venture capital activity in India and Indian-founded companies worldwide. View sample issues of Venture Intelligence India newsletters and reports.
The good way is to recruit one or more people to the company early on, spend time with them infusing them with your passion and vision, getting them familiar with the technology and culture, and gradually giving them the keys to the car.
The handoff of power should be so incremental that nobody can point to a date at which it happened.
There will always be an official date when someone takes the CEO title, but it should happen when its already a defacto title.