The reason I ask is because of the problem I have been having:

http://www.grandprix.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=005530;p=0&r=nfx

Does vapor lock ever happen on modern vehicles?

I'm going to say no, it's not likely to happen on our cars.

Vapor lock happens in older cars with float bowls, and FP's that are mounted to the side of the engine. In hot weather, the extreme temps will cause the fuel to boil in the Fuel Pump, or the float bowls in a Carbureter.
Our cars have no reservoir as a carbureter float bowl, and the fuel pump is in the gas tank, making vapor lock highly unlikely.... Even if gas in the lines boil, I would imagine that it would only cause a stutter as the fuel is constantly being circulated from the tank to the fuel rails and back to the tank.