In the USA, [OnStar](http://www.onstar.com/) have an online diagnostics database that is set up to email you with car maintenance reminders.
The site has over 1 million subscribers already after only 6 months.
The advantage is that you can save some scheduled trips to the workshop because real data about wear-and-tear and fluid levels more accurately predicts when a service is needed.
To use the service, your car will need some factory installed hardware.