Twice! The first time was in Blue (I could have quit early, I had filled the whole Pokedex except for Blastoise, but because I had a Mew the game calculated it as a full 150) and I was entirely unimpressed with my reward. The second time was in Silver, which was a much slower and more infuriating process because of all the happiness-based evolutions. Crobat was the last one I got.
I might be close to a full Pokedex again this gen, since I've sent over all 1,000+ Pokemon from gen 3 onward into the Bank, I'm probably just missing some middle evolutions here and there, as well as the soon-to-be-released gen 6 legendaries.