I played Crystal version for over 200 hours, never really seeing anything special, but then my friend Michael played Silver for literally about 12 and caught 3 shinies (yes, including Red Gyarados). One of them happened to be one of my favorite Pokemon at the time: Zubat. I think I almost threw my game away when that happened.
It once took me 2 hours to catch Regice on my Sapphire version. Hundreds upon hundreds of Pokeballs and quite a few resets. I still don't know why I wasted all that time. Similar situation with the Moltres in Fire Red. Didn't take quite so long, but I had fewer Pokeballs and weaker Pokemon, so I had to reset more often and make sure it didn't kill my team.
Another Michael story, he's the only person I've ever known to legitimately get PKRS in his game, Ruby version. Going back to his insane luck with shiny Pokemon, he also got a shiny Tyrogue in Crystal (from the mystery egg, I believe), which he then used the cloning glitch on to get shiny versions of all three of its evolutions. Found a shiny Psyduck on Diamond, too. Seriously, it's like they just come out of his ass.