I've done it on Platinum and am slowing working my way through it on White. I've very nearly finished the Unova PokéDex (complete with one of each Pokémon in Dex order), all I'm missing is Deino line, Landorus and Kyurem.
However I only recently realised how much 649 is. That's heaps of Pokémon and it will certainly take to Pokéshift, trade, train, evolve and breed to get one of each Pokémon.
Because I'm Forever Alone I have to finish it all by myself, but by no means an impossible feat, the way I see it, the more Pokémon there are the more rewarding it is to finish the PokéDex.