I know they take a while to build up but can anything stop a fleet of these? they seem a tad overpowered. What do you guys think?

I'm by no means a skilled player but in the short time I played the beta, this so-called "carrier fleet" would require a 40+ minute match. I'm having trouble envisioning a match against a protoss player taking that long as any other race, with proper map control.

 Things that beat Carriers:
 
Void Rays (big damage after powered up) 
Corrupters (extra damage to Massive + damage debuff ability) 
Battlecrusiers (Yamato Cannon focus fire) 
Vikings (out ranges Carriers, could take out mass Carriers with inferior numbers with proper kiting) 
Armor Upgrades (Carriers attack fast with small hits, units with high armor take very little damage from them.  A good player would have level 3 armor for their units around the time that Carriers show up.) 

As it stands right now, Colossi, High Templar, and Void Rays are better choices for Protoss late game units.