I have over 50K miles on my 06 Mazda3s, and I've had no issues at all though I do all the maintenance myself and the car has never been to a mechanic for anything other than warranty work.
Some of the warranty work that was done prior to hitting the 50K mark was:
Passenger Engine Mount leaking and busted and 3 CEL's for Purge Solenoid valve (The last visit the dealer just got rid of the CEL permanently without fixing it cause they had no purge valves in stock, haha)
Here's the maintenance I've done, keep in mind everyone has their own schedules, and this is just one I came up with on my own so it's not Mazda's or the best...
Replace Coolant with longlife Peak Global Lifetime stuff, or extended life coolant. (First flush at 30K miles, next flush every 50K miles)
Replace Transmission fluid with Mercon V or M-V. (Every 25K miles)
Oil Changes every 7K miles
Change Air filter every 25K miles with my CAI (Or Clean it with K&N Recharge)
Replace Power Steering Fluid with Mercon V. (every 50K miles)
Replace Brake Fluid (Every 30K miles)
Sea Foamed the engine
Tried Shell V-power and Techron fuel additive
Will replace spark plugs at 75K miles.
So far my thermostat has been fine, but if it does go then I'll know to just replace it. Somebody on the forums said it was pretty easy to do if I remember.
Those are the major things. Don't let the dealer charge you extra for misc garbage like inspecting tires and lubricated hinges and locks. That sort of thing can be done by yourself and they just spray the hinges with silicone dry lube and check the treads if you are on the wear indicators.
If you get nit picky, you can hand choose what services you want done and this should save you some money.
I think most of the time the full circle inspections are free... Why? Because the dealer wants to find out any little thing wrong with your car so they can make some money fixing it. Even if it's warranty related work... It's still work.