No, i have a 185mm disc front (4 piston) and 165 rear (2 piston). But you can run same size discs no problems. Most cross country guys run same size front and rear - i came from more of a DH background and already had the 185 front and liked its awesome stopping power.
Depends what you mean "real life" i suppose. I'd put them on a normal commuter bike for the lack of maintenance alone, despite barely using brakes on a commute. If you're talking just a ride round the corner to the shops - its probably just going to add stealability to your bike.
I've never yet known anyone who tried discs go back to rim brakes. I spent ages convincing my mate to try them, even offered to buy them off him if he didnt like them. Needless to say they stayed on lol. They are more progressive but ultimately more reliable feel-wise. If you squeeze lighly you can drag a nice long drag but if you pull hard you know you'll get a proportional stopping power. With V's i found that you could control speed nicely but if you really needed to stop you pull hard and find you get frame flex (rears) and cable stretch, meaning you need to input a disproportionate amouint of force to get the same stopping power. But ultimate stopping is not the point really - we can all lock brakes on a bike (though i had never locked the front until i got the 4pots!) but IMO its just a nice, more progressive and reliable stopping feel. You know that even when you go plunging through puddles and rivers you can still stop as well as before.
I spent ages with Hydraulic rim brakes, they're the half-way-house and work nicely until you get ice buildup or lots of mud, or if you have a lightweight frame - they are so powerful ive moved the rear seat stays apart by 15mm with my hydro rim brakes - obviously losing half the stopping power. Then you need frame braces to stop the flex which adds weight to your bike again etc etc.
If you get cheaper ones you can end up with caliper flex that loses half of the point of them, and cable actuated discs really dont have much point TBH but good hydraulics are only a little more than good cable V's so in my opinion theres little point going with the V unless you dont have the mount points on your frame.
J