I bought BEAT LT(Petrol) back in Aug2010. Its been close to 1.5 years and I have got around 20000kms on it. The experience so far has been awesome in all respects. City driving is a pleasure to deal with whereas on highways, its much more than that.
Mileage - 15(with A/C) in city and believe me its 18+(with A/C) on highways. You just need to shift at appropriate times.
Service - Very good service experience so far. Every time, my car was taken for service, it was handled very well and delivered on time. The quality of service also, has been promising so far. It does depend on the service center also where you are taking your car which in my case was the one named Autovikas at Peeragarhi, West Delhi. They have got good technicians and equipment to provide a good service. They also organize events like games etc. for the people waiting in customer lounge while their cars are being serviced so that the customers dont get bored.
Boot space - Definitely less but it was not a concern for me.
Overall, I would say that I am very satisfied with the car and would highly recommend to people looking for a car in this segment.