Ancestry yesterday. It holds 8697 personnel records of former Guinness employees dating from 1824 to 2002 and includes details such as name, dates of birth and death, the date and age when an employee joined the company, and, where relevant, a spouse's name.
This data is taken from the Guinness website where this collection can be searched free of charge. You may also find additional information on the Guinness site, including references, publication information, comments, historical context, and even images. Presumably the purpose of the duplication via Ancestry is to help make this resource more widely known.
The Guinness database holds more than 20,000 records, so I'm assuming the Ancestry collection will be updated and added to in due course.