Hi Frank,
There are potentially a few flaws on the carrera. The most obvious is the blue screws in the movement which you can see through the clear caseback, these can be easily swapped with Gen ETA 7750 screws.
The next would be the TAG Heuer logo. Sometime the "G" in the logo is missing the little arrows on the end. I bought one of the none day carreras from Trevor which has the arrows and a pretty good replication of the dial, but the day dates often miss this as far as I'm aware.
The next two issues are less obvious, but definately there. The day/datewheel font is wrong, very wrong at that, but this can again be easily swapped for a gen ETA datewheel from ebay for around £12 each. The biggest killer of all if you are really anal, and I am is the geneve stripes on the rotor. On the rep they have an even number of stripes, but the gen they have an odd number.
Have a look of Trevors site what I mean about the stripes on the rotor compared to the gen.
http://www.trwatch.com/product_info.php?cPath=49&products_id=530
http://www.ablogtoread.com/wp-content/uploads/2011/09/TAG-HEUER-CARRERA-RING-MASTER-back.jpg
When I get time I will do a proper reveiw of the Carrera Cal 16 and highlight these flaws, but to be honest it is very close our of the box and by swapping the day/datewheels and the screws you can easily have a very high quality rep.
HTH