Compared to BMW and MErcedes, the IS-F is undoubtly cheaper to run: cheaper insurance, better mpg. Brake and tyres on a side note are probably the same, be prepared to change before 20k miles if you like to use the right foot :P
All the (little) problems I have had have been taken cre of under warranty. As fjcfarrar, I subscribed to the Extracare warranty/assistance expansion to be safe but I doubt I will have to use it.
Services are almost the same as for the IS250, it just needs more oil.