Oh yeah, guys? I'm almost certain now that Shaymin isn't supposed to be a legendary, just a rare, one-time-chance Pokemon. You know how Dialga/Palkia, Darkrai, Giratina...every legendary has some sort of epic music? Shaymin's music? The normal wild Pokemon music.
And yeah, I know, I hack. I used my Action Replay's Walk Through Walls code to get to Shaymin (I was doing it again so I could catch it in Pearl so my Pearl trainer is the OP, thus averting any disobedience).
Also, I fully inted to train it up really high and beat the entire Elite 4 with it. My friend suggested it to me, and I sort of like the idea.
Heck, my only gripe with Shaymin thus far is that its movepool is pretty poor. It can still learn Psychic, though, which is nice.